Add negative tests for deleting attached volume

Due to lack of an error handling, Nova's delete-volume API returns
HTTP500 error when deleting an attached volume.
This patch adds the corresponding test for reproducing the problem
on the gate and blocking the same issue in the future.

Change-Id: Idb6267be770bcf2541595babebf269cdc71c2b8d
Depends-On: Ia07556b2dc18678baa4c8fbd65820d8047362ef9
Related-Bug: #1630783
1 file changed