Add exception handling for copy_volume_to_image()

The method require_driver_initialized occurs exception so that the
method volume_get will be not executed, and the variable 'volume'
will be not defined. In the "finally" code segment, the
volume['instance_uuid'] will get the UnboundLocalError, this patch
gets volume before require_driver_initialized to avoid the above
problem.

Change-Id: Ic8167383eb67c5016c9853da274455e0f202dc4d
Closes-Bug: #1322958
Fix a message format error in migration cleanup

In some situations, the volume migration failed. After the cleanup
begin, code was trying to format a string value as an int,
this caused "copy_error = True" not being invoked, resulted
in UnboundLocalError exception.

Change-Id: I445394cc06fe221804901e8014d60e870f0fe2f7
Closes-Bug: #1290317
Merge "Fix a message format error in migration cleanup"
Merge "Add exception handling for copy_volume_to_image()"