Remove unnecessary metadata from the 3PAR drivers

Currently, both the HP 3PAR iSCSI and FC drivers are populating
the volume and snapshot metadata field with unnecessary data that
should actually be stored on the backend. This data should not be
accessible by the user which it is today and could be updated as well.

This patch will remove all custom 3PAR data from the metadata fields.

Change-Id: I3086be3856192a27fa1db1ada89d95c290c68df7
Fixes: bug 1203144