Comment 6 for bug 1536337

I got the same with 1.25.6, also in an automated run and I don't have /var/log/syslog from the bootstrap node.

This is the last bit of the bootstrap output:
Reading state information...
cloud-image-utils is already the newest version.
cloud-image-utils set to manually installed.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Reading package lists...
Building dependency tree...
Reading state information...
tmux is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Attempt 1 to download tools from https://streams.canonical.com/juju/tools/agent/1.25.6/juju-1.25.6-trusty-amd64.tgz...
tools from https://streams.canonical.com/juju/tools/agent/1.25.6/juju-1.25.6-trusty-amd64.tgz downloaded: HTTP 200; time 4.449s; size 18647709 bytes; speed 4191636.000 b
ytes/s Tools downloaded successfully.
b3a6c835e28902b302f65be08d944252136c0b1bc015953cd6c51f246c4a3e1e /var/lib/juju/tools/1.25.6-trusty-amd64/tools.tar.gz
2016-08-18 17:24:04 INFO juju.cmd supercommand.go:37 running jujud [1.25.6-trusty-amd64 gc]
2016-08-18 17:24:04 INFO juju.network network.go:242 setting prefer-ipv6 to false
2016-08-18 17:24:05 INFO juju.agent identity.go:22 writing system identity file
2016-08-18 17:24:05 INFO juju.mongo mongo.go:208 Ensuring mongo server is running; data directory /var/lib/juju; port 37017
2016-08-18 17:24:05 INFO juju.mongo mongo.go:372 installing juju-mongodb
2016-08-18 17:24:05 INFO juju.utils.packaging.manager utils.go:57 Running: apt-get --option=Dpkg::Options::=--force-confold --option=Dpkg::options::=--force-unsafe-io --
assume-yes --quiet install juju-mongodb
2016-08-18 17:29:11 INFO juju.worker.peergrouper initiate.go:78 finished MaybeInitiateMongoServer
2016-08-18 17:29:11 ERROR juju.cmd supercommand.go:429 cannot initiate replica set: cannot dial mongo to initiate replicaset: no reachable servers
ERROR failed to bootstrap environment: subprocess encountered error code 1
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