Add CHAP support for 3PAR ISCSI

Adds CHAP support to 3PAR ISCSI.  Volume metadata will store
CHAP credentials to allow volumes to be attached to hosts on
a 3PAR backend.  Credentials are generated when the first volume
is attached.  Subsequent volumes lookup the CHAP credentials
from an existing volume already attached to the host.

Implements: blueprint add-chap-support-3par-iscsi
DocImpact

Change-Id: I45d77c4243339e8fc76969042634c6c45899fbae
Merge "Add CHAP support for 3PAR ISCSI"