Reduce the redundant variable declarations

The method create() in /cinder/api/v2/volumes.py has two redundant
variable declarations: image_href = None image_uuid = None
These should be reduced

Change-Id: If3798d4bd96998707d7a5f87ece95ed8c93cc042
Closes-bug: #1265148
Merge "Reduce the redundant variable declarations"