Fixed bug with unxpected stack delete

* Fixes issue when existing stack has been deleted unxpectedly if cluser which
  is being deleted has the same name
* Issue has been resolved on validation level
* Unit-tests were added

Change-Id: Ifbfb1aebe78c2274f9d85f08992fb13d32a3e46b
Closes-Bug: #1286082
Merge "Fixed bug with unxpected stack delete"