Code review comment for lp://staging/~thedac/charmsupport/volume-management

The code attempts to avoid executing realtion-ids with no reltype.

relation-ids with no reltype produces:

root@juju-stagingstack-u1-musicsearch-instance-9:/var/lib/juju/units/u1-msearch-be-1-1/charm# relation-ids
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1039, in _inlineCallbacks
    result = g.send(result)
  File "/usr/lib/juju/juju/juju/hooks/commands.py", line 132, in run
    raise MustSpecifyRelationName()
juju.hooks.protocol.MustSpecifyRelationName: Relation name must be specified
2013-04-24 16:09:31,686 ERROR: Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1039, in _inlineCallbacks
    result = g.send(result)
  File "/usr/lib/juju/juju/juju/hooks/commands.py", line 132, in run
    raise MustSpecifyRelationName()
juju.hooks.protocol.MustSpecifyRelationName: Relation name must be specified

2013-04-24 16:09:31,687 ERROR: [Failure instance: Traceback: <class 'juju.hooks.protocol.MustSpecifyRelationName'>: Relation name must be specified
/usr/lib/python2.7/dist-packages/twisted/internet/defer.py:545:_runCallbacks
/usr/lib/juju/juju/juju/hooks/cli.py:190:_run
/usr/lib/python2.7/dist-packages/twisted/internet/defer.py:134:maybeDeferred
/usr/lib/python2.7/dist-packages/twisted/internet/defer.py:1181:unwindGenerator
--- <exception caught here> ---
/usr/lib/python2.7/dist-packages/twisted/internet/defer.py:1039:_inlineCallbacks
/usr/lib/juju/juju/juju/hooks/commands.py:132:run
]