Implement Clone CG in Pure Volume Drivers

Implement Clone CG in Pure Volume Drivers

This adds support for the consisgroup-create-from-src method specifying
a source consistency group.

The driver will create a new Purity Protection Group, take a temporary
snapshot of the source Protection Group, create new volumes from the
consistent snapshot, and then add these new volumes into the newly
created protection group.

Implements: blueprint pure-clone-cg
Change-Id: I3446c4a86027f1f50ada673ddb1f3b13b5e8f6cc