Remove unused variable in restore_backup method

Variable err in restore_backup method is not being used, so remove this
'err ' variable.

Change-Id: I31f6da5fd55e025d6496aca76a1157ff5a167d9e
Closes-Bug: #1270034
Merge "Remove unused variable in restore_backup method"
(Test commit) Change README to reflect Jio's fork of Cinder

Change-Id: I3f26c0a736e63725aec24ca2fa12c707b8e6460f