Add negative test for attaching an attached volume to the same instance

This scenario came up during the volume multi-attach spec review in
Nova and is something we should be sure is not allowed with a
volume that is already attached since Nova does not yet support
volume multi-attach.

Change-Id: I98e25554d39449178df696a0d90cc62b662eda24
Depends-On: Ifc01dbf98545104c998ab96f65ff8623a6db0f28
1 file changed