Remove instance power-off in delete function

In case if instance deleteion fails we try
to reset instance state, nova power-off action
was invokes, that leads to the raise of
UnexpectedTaskStateError_Remote

In this patch invocation of power-off was deleted
Now, we do several retries for deleteion and
if instance fails to be deleted - fail the test

Change-Id: Ic059d976a6a312fa32a90fa24b439e133031780e
Closes-bug: #1285094
Merge "Remove instance power-off in delete function"