Add missing LH SAN driver features for Havana

The LeftHand driver did not support snapshot or extend volume.
The following features are part of the minimum driver features
that should be implemented in every cinder driver. This patch
adds the following missing features;
create snapshot
delete snapshot
create volume from snapshot
extend volume
It also fixes the DocStrings in the unit test so they pass the
checks.

Change-Id: Icda790fcddf4ea11782a8d6ec57b1e8f871eb167
Fixes: bug 1217118
Merge "Add missing LH SAN driver features for Havana"