Fixed nova VM live migration issue with 3PAR

Fixed nova VM live migration issue with 3PAR

Nova bypasses the cinder checks for a volume
being available, when it tries to attach a volume
to a new host during live migration.  The assumption
in cinder to this point has been that volumes can only
be attached to one host.  The 3PAR driver worked under
that assumption.  This assumption fell apart during detach
time as the driver was only looking for a VLUN on the
entire 3PAR, since it assumed it could only exist on one host.

This patch ensures that the driver looks for the VLUN on the
hostname it expects.

Change-Id: Ie894ad386990794d270ca1cb72f40095bd40c2e6
Closes-Bug: 1288927