fix volume swap exception cases

Currently when the target instance id doesn't match with the instance_id of the
volume to be replaced VolumeUnattached is raised, and InvalidVolume would be a
fittest response.
In the other hand, currently, when the volme to be replaced is not attached at
all InvalidVolume is raised, and VolumeUnnatached would be a fittest response.

Change-Id: I661b97762af70765ab8111313d24cf1a175f7e6c
Merge "fix volume swap exception cases"