Ensure rbd connect exception is properly caught

If the rbd driver fails to connect to Ceph the exception
was not being properly caught resulting in the volume
remaining in the 'creating' state until the corresponding
task eventually times out (on top of the time it took
for the connect to fail).

Also added config option for rados connect timeout.

DocImpact: new config option 'rados_connect_timout'
Closes-Bug: 1211839
Change-Id: I5e6eaaaf6bed3e139ff476ecf9510ebe214a83f9
Merge "Ensure rbd connect exception is properly caught"