Fix volume related operation in CloudByte driver

Fix volume related operation in CloudByte driver

Currently the volume related operation in CloudByte driver does not:

* Update the ISCSI Initiator Group during volume deletion operation,
and
* During retry of any volume operation it does not catches the exact
cause of the failure happened.

So to deal with the following issues two changes has been done in
CloudByte Driver:

* Added a new method "_update_initiator_group"
ISCSI Initiator Group is one of the parameter added to the volumes
at the time of creation in CloudByte Storage. Using this the external
source can access the volumes easily. By default, Initiator Group
value is set to 'ALL', but it should be changed to 'None' before
deletion. Since the following is not happening, thus volume delete
operation fails from OpenStack. In order to avoid this the
"delete_volume" method now uses the "_update_initiator_group" which
update the volume ISCSI Initiatior Groupof the volumes to 'None'
before deletion, and thus volume delete operation will have no issues
while running from OpenStack.

* Added a check to "_retry_volume_operation"
The _retry_volume_operation method was not able to check the exact
cause of the failure happened during volume operation in CloudByte
Storage, which arises if some invalid parameters are provided in
"cinder.conf" against "cloudbyte backend" or if some anomaly happens
at CloudByte Storage during any volume operation from OpenStack. Due
to this, tracking the ERROR becomes a very difficult task to do. Thus
to resolve this issue a "check" has been added to the method which
will raise the exact cause of the error and thus making it easier to
solve.

Change-Id: Ie385df7c18520ea4abb5640fb354bdd18212c5a3
Closes-Bug: #1499297