Comment 6 for bug 1503715

Reviewed: https://review.openstack.org/233294
Committed: https://git.openstack.org/cgit/openstack/murano/commit/?id=e6b7ccb8985e3da1f947deb9cc3618173f076d19
Submitter: Jenkins
Branch: master

commit e6b7ccb8985e3da1f947deb9cc3618173f076d19
Author: Stan Lagun <email address hidden>
Date: Sat Oct 10 01:33:22 2015 +0300

    Do not try to delete server from deleted Heat stack

    Because now Environment's .destroy method would
    be called before that of an Instance the later will try
    to delete itself from the stack that is physically not
    existing and represented as an empty dictionary in
    HeatStack.current().

    With this change Instance will check stack existence
    before deleting anything.

    Also a method to check if Instance is present in Heat
    stack template was added so that application could check
    if it is safe to use the instance (for example to send Agent plans)

    Change-Id: I298f3f079a153ef87ed7213b7f1432c9e5e4b4b6
    Closes-Bug: #1503715