3PAR: Raise Ex when del snapshot with depend vol

Deleting a 3PAR snapshot can result in an HTTP Conflict error message,
such as when a volume is dependent on it.
Previously, this exception was not caught, and the state was set
to "Error_Deleting" with no recovery path.
The code was updated to catch this exception and raise a
SnapShotIsBusy exception with an appropriate error message.
The state reverts back to 'Available' allowing the user to try again
after removing the dependency.

Change-Id: Ibe8c5d581af10c85397c37993c49f8fc3bce8620
Closes-Bug: #1250249
Merge "3PAR: Raise Ex when del snapshot with depend vol"