I grabbed the patch and tried to deploy just a single instance. That single instance came up without issues.

Then using juju add-unit, I started another two nodes. One joined the cluster successfully, the other seems to be hanging on:

Clustering with remote rabbit host (rabbit@juju-machine-17-lxc-0).

Tail end of the JuJu logs:

Reading package lists... Doneter-relation-changed 
Building dependency tree       r-relation-changed 
Reading state information... Donerelation-changed 
2016-05-24 14:40:37 INFO worker.uniter.jujuc server.go:173 running hook tool "status-set" ["maintenance" "Clustering with remote rabbit host (rabbit@juju-machine-17-lxc-0)."]
2016-05-24 14:40:37 DEBUG worker.uniter.jujuc server.go:174 hook context id "rabbitmq/3-cluster-relation-changed-383633683969241899"; dir "/var/lib/juju/agents/unit-rabbitmq-3/charm"
2016-05-24 14:40:37 INFO worker.uniter.jujuc server.go:173 running hook tool "juju-log" ["-l" "DEBUG" "Running ['/usr/sbin/rabbitmqctl', 'stop_app']"]
2016-05-24 14:40:37 DEBUG worker.uniter.jujuc server.go:174 hook context id "rabbitmq/3-cluster-relation-changed-383633683969241899"; dir "/var/lib/juju/agents/unit-rabbitmq-3/charm"
2016-05-24 14:40:37 DEBUG juju-log cluster:65: Running ['/usr/sbin/rabbitmqctl', 'stop_app']
2016-05-24 14:40:37 INFO cluster-relation-changed Stopping node 'rabbit@juju-machine-13-lxc-3' ...

It never seems to stop.

Full process list:

root@juju-machine-13-lxc-3:/var/log/juju# ps auxwww
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.0  37540  5676 ?        Ss   14:36   0:01 /sbin/init
root        48  0.0  0.0  35276  8056 ?        Ss   14:36   0:00 /lib/systemd/systemd-journald
root        86  0.0  0.0 274488  6208 ?        Ssl  14:36   0:00 /usr/lib/accountsservice/accounts-daemon
syslog      87  0.0  0.0 260632  3244 ?        Ssl  14:36   0:00 /usr/sbin/rsyslogd -n
root        88  0.0  0.0  27728  2972 ?        Ss   14:36   0:00 /usr/sbin/cron -f
root        92  0.0  0.0  28548  3024 ?        Ss   14:36   0:00 /lib/systemd/systemd-logind
daemon      97  0.0  0.0  26044  2284 ?        Ss   14:36   0:00 /usr/sbin/atd -f
message+    98  0.0  0.0  42948  4016 ?        Ss   14:36   0:00 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
root       103  0.0  0.0 277180  6120 ?        Ssl  14:36   0:00 /usr/lib/policykit-1/polkitd --no-debug
root       274  0.0  0.0  65612  6244 ?        Ss   14:36   0:00 /usr/sbin/sshd -D
root       278  0.0  0.0   5224   160 ?        Ss   14:36   0:00 /sbin/iscsid
root       279  0.0  0.0   5724  3536 ?        S<Ls 14:36   0:00 /sbin/iscsid
root       303  0.0  0.0  14476  2180 pts/3    Ss+  14:36   0:00 /sbin/agetty --noclear --keep-baud pts/3 115200 38400 9600 vt220
root       305  0.0  0.0  14476  2284 lxc/console Ss+ 14:36   0:00 /sbin/agetty --noclear --keep-baud console 115200 38400 9600 vt220
root       308  0.0  0.0  14476  2140 pts/0    Ss+  14:36   0:00 /sbin/agetty --noclear --keep-baud pts/0 115200 38400 9600 vt220
root       310  0.0  0.0  14476  2180 pts/2    Ss+  14:36   0:00 /sbin/agetty --noclear --keep-baud pts/2 115200 38400 9600 vt220
root       311  0.0  0.0  14476  2124 pts/1    Ss+  14:36   0:00 /sbin/agetty --noclear --keep-baud pts/1 115200 38400 9600 vt220
root       681  0.0  0.0  19696  3304 ?        Ss   14:36   0:00 bash /var/lib/juju/init/jujud-machine-13-lxc-3/exec-start.sh
root       685  0.0  0.0 1649380 58932 ?       Sl   14:36   0:00 /var/lib/juju/tools/machine-13-lxc-3/jujud machine --data-dir /var/lib/juju --machine-id 13/lxc/3 --debug
root       770  0.0  0.0  19696  3280 ?        Ss   14:36   0:00 bash /var/lib/juju/init/jujud-unit-rabbitmq-3/exec-start.sh
root       774  0.0  0.0 1568768 61784 ?       Sl   14:36   0:02 /var/lib/juju/tools/unit-rabbitmq-3/jujud unit --data-dir /var/lib/juju --unit-name rabbitmq/3 --debug
rabbitmq 16455  0.0  0.0   4508   716 ?        Ss   14:39   0:00 /bin/sh /usr/sbin/rabbitmq-server
rabbitmq 16463  0.0  0.0   4508  1756 ?        S    14:39   0:00 /bin/sh -e /usr/lib/rabbitmq/bin/rabbitmq-server
rabbitmq 16570  0.0  0.0  26304  2124 ?        S    14:39   0:00 /usr/lib/erlang/erts-7.3/bin/epmd -daemon
rabbitmq 16773  0.0  0.0 5258856 106724 ?      Sl   14:39   1:52 /usr/lib/erlang/erts-7.3/bin/beam.smp -W w -A 64 -P 1048576 -K true -B i -- -root /usr/lib/erlang -progname erl -- -home /var/lib/rabbitmq -- -pa /usr/lib/rabbitmq/lib/rabbitmq_server-3.5.7/sbin/../ebin -noshell -noinput -s rabbit boot -sname rabbit@juju-machine-13-lxc-3 -boot start_sasl -config /etc/rabbitmq/rabbitmq -kernel inet_default_connect_options [{nodelay,true}] -sasl errlog_type error -sasl sasl_error_logger false -rabbit error_logger {file,"/<email address hidden>"} -rabbit sasl_error_logger {file,"/<email address hidden>"} -rabbit enabled_plugins_file "/etc/rabbitmq/enabled_plugins" -rabbit plugins_dir "/usr/lib/rabbitmq/lib/rabbitmq_server-3.5.7/sbin/../plugins" -rabbit plugins_expand_dir "/var/lib/rabbitmq/mnesia/rabbit@juju-machine-13-lxc-3-plugins-expand" -os_mon start_cpu_sup false -os_mon start_disksup false -os_mon start_memsup false -mnesia dir "/var/lib/rabbitmq/mnesia/rabbit@juju-machine-13-lxc-3" -kernel inet_dist_listen_min 25672 -kernel inet_dist_listen_max 25672
rabbitmq 17005  0.0  0.0   7504   912 ?        Ss   14:39   0:11 inet_gethost 4
rabbitmq 17006  0.0  0.0  13856  1992 ?        S    14:39   0:23 inet_gethost 4
root     26590  0.0  0.0 129484 60504 ?        S    14:40   0:01 /usr/bin/python /var/lib/juju/agents/unit-rabbitmq-3/charm/hooks/cluster-relation-changed
root     27360  0.0  0.0   4508  1576 ?        S    14:40   0:00 /bin/sh /usr/sbin/rabbitmqctl join_cluster rabbit@juju-machine-17-lxc-0
root     27369  0.0  0.0  49344  3160 ?        S    14:40   0:00 su rabbitmq -s /bin/sh -c /usr/lib/rabbitmq/bin/rabbitmqctl  "join_cluster" "rabbit@juju-machine-17-lxc-0"
rabbitmq 27370  0.0  0.0   4508   712 ?        Ss   14:40   0:00 sh -c /usr/lib/rabbitmq/bin/rabbitmqctl  "join_cluster" "rabbit@juju-machine-17-lxc-0"
rabbitmq 27371  0.0  0.0 1276856 71508 ?       Sl   14:40   0:00 /usr/lib/erlang/erts-7.3/bin/beam.smp -- -root /usr/lib/erlang -progname erl -- -home /var/lib/rabbitmq -- -pa /usr/lib/rabbitmq/lib/rabbitmq_server-3.5.7/sbin/../ebin -noshell -noinput -hidden -boot start_clean -sasl errlog_type error -mnesia dir "/var/lib/rabbitmq/mnesia/rabbit@juju-machine-13-lxc-3" -s rabbit_control_main -nodename rabbit@juju-machine-13-lxc-3 -extra join_cluster rabbit@juju-machine-17-lxc-0
rabbitmq 27592  0.0  0.0   7504   896 ?        Ss   14:40   0:00 inet_gethost 4
rabbitmq 27593  0.0  0.0  13856  1728 ?        S    14:40   0:00 inet_gethost 4
root     28048  0.0  0.0  95460  7108 ?        Ss   14:48   0:00 sshd: ubuntu [priv]
ubuntu   28050  0.0  0.0  45108  4872 ?        Ss   14:48   0:00 /lib/systemd/systemd --user
ubuntu   28051  0.0  0.0  60992  1664 ?        S    14:48   0:00 (sd-pam)
ubuntu   28084  0.0  0.0  95460  4072 ?        R    14:48   0:00 sshd: ubuntu@pts/4
ubuntu   28085  0.0  0.0  21176  5028 pts/4    Ss   14:48   0:00 -bash
root     28118  0.0  0.0  55756  3952 pts/4    S    14:48   0:00 sudo su
root     28119  0.0  0.0  51004  3436 pts/4    S    14:48   0:00 su
root     28120  0.0  0.0  19920  3692 pts/4    S    14:48   0:00 bash
root     28391  0.0  0.0  36084  3224 pts/4    R+   14:50   0:00 ps auxwww