Remove db access from 3PAR and LH cg functions

Remove db access from 3PAR and LH cg functions

The HP 3PAR and HP LeftHand drivers no longer need to access the db in
order to grab snapshots and volumes for the following functions:
* delete_consistencygroup
* create_cgsnapshot
* delete_cgsnapshot

This patch removes all db access at the driver level for both 3PAR and
LeftHand drivers.

Change-Id: I2e29366573f53cf6e61939381bde5d04f188f42d