4.0 fixes: Add timeout between volume and instance deletion

Make next changes in smoke.test_volumes.py:
* Make volume detach trough nova client
* Add verification that volume really deleted
  before deletion of instance

Closes-Bug: #1250231

Change-Id: If1dd2408cdf14f7a562ea8d5a447681d2c42df95
Merge "4.0 fixes: Add timeout between volume and instance deletion" into stable/4.0