Fixes the 3PAR drivers CPG validation

Fixes the 3PAR drivers CPG validation

The 3PAR drivers were not checking if the Common Provisioning
Group(CPG) exists in the virtual domain at volume create time when
the default was being overwritten by volume type extra_specs value.
It was also reporting the default CPG in the metadata returning
after creating the volume. Now it reporting the correct CPG and
setting the correct snapshot cpg if different from the default
or not set.

Fixes bug 1186427

Change-Id: Idef7a4f29854c82980789786f2414e5046c8d8fb