This charm assumes a location on disk that only works with pyjuju, but not juju-core:
2013-07-26 21:39:00 DEBUG juju server.go:106 worker/uniter/jujuc: hook context id "rabbitmq-server/0:ceph-relation-changed:7253652461340230885"; dir "/var/lib/juju/agents/unit-rabbitmq-server-0/charm"
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK Traceback (most recent call last):
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK File "/var/lib/juju/agents/unit-rabbitmq-server-0/charm/hooks/ceph-relation-changed", line 302, in <module>
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK utils.do_hooks(hooks)
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK File "/var/lib/juju/agents/unit-rabbitmq-server-0/charm/hooks/lib/utils.py", line 28, in do_hooks
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK hook_func()
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK File "/var/lib/juju/agents/unit-rabbitmq-server-0/charm/hooks/ceph-relation-changed", line 234, in ceph_changed
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK ha_joined()
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK File "/var/lib/juju/agents/unit-rabbitmq-server-0/charm/hooks/ceph-relation-changed", line 181, in ha_joined
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK openstack.save_script_rc(**env_vars)
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK File "/var/lib/juju/agents/unit-rabbitmq-server-0/charm/hooks/lib/openstack_common.py", line 226, in save_script_rc
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK with open(juju_rc_path, 'wb') as rc_script:
2013-07-26 21:39:00 INFO juju context.go:221 worker/uniter: HOOK IOError: [Errno 2] No such file or directory: '/var/lib/juju/units/rabbitmq-server-0/charm/scripts/scriptrc'
it should use CHARM_DIR instead of a hardcoded path.
It was merged in r42.