Using extra-specs in cloned vols for Nimble driver

Using extra-specs in cloned vols for Nimble driver

This patch uses the set extra-specs while cloning a volume. All
existing extra-specs: 'nimble:encryption', 'nimble:perfpol-name'
and 'nimble:multi-initiator' are being reflected in the cloned
volume.

In the existing code, the extra-specs were not being considered
while cloning volumes; the parent volume attributes were used
directly in the cloned volume. This patch uses the extra-spec
values if they are set or if not then uses the default values
for the same.

Change-Id: I7610377e557720038f77ebd318422456e658e2ce
Closes-Bug: #1507821