Local cache feature of Oracle ZFSSA drivers

Local cache feature of Oracle ZFSSA drivers

The feature enables ZFSSA drivers to create and reuse cache volumes
on ZFSSA backends. It takes advantage of ZFSSA snapshot and clone,
which can be created almost instantly from an existing volume.

Cache volumes will be removed if it has no clone. Custom schemas
and WebDAV properties are used to store cache volumes' properties.

DocImpact
Change-Id: I06b21a3f760abf540246971c00d923eda8fe57e3
Implements: blueprint oracle-zfssa-local-cache