VMware: fix bug for exceptions thrown in _wait_for_task

If the _call_method fails, for example a resource is not found,
then the same call will be invoked again due to the fact that the
polling task was not stopped.

Closes-Bug: #1246848

Change-Id: If4818e41aed5be03395ab22afc0edf9abb3c34e1
(cherry picked from commit 1c1570ff7ac8470d7dba28c893300835b22e0966)