Prevent unnecessary stack.push in Instance::releaseResources

[Konstantin]

During the removal of the Environment with a lot of Instances, `releaseResources` called for each of the Instances. This causes push of new stack template (without next Instance) into Heat for each call. But stacks of each `CloudRegion` will be deleted, so we can skip each call of `push()`.
Thus entire `HeatStack::push()` operation is unnecessary.

[Valerii Kovalchuk (vakovalchuk)]

https://review.openstack.org/#/c/377972/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/377972
Committed: https://git.openstack.org/cgit/openstack/murano/commit/?id=510583ffff1c692d713a4f469bf72c45cde5f773
Submitter: Jenkins
Branch: master

commit 510583ffff1c692d713a4f469bf72c45cde5f773
Author: Snihyr Kostyantyn <email address hidden>
Date: Tue Sep 27 21:58:24 2016 +0300

    Prevent unnecessary stack.push in Instance::releaseResources

    All stack resources will be released if current CloudRegion object
    should be destroyed (isDoomed). There is no reason to push stack into Heat
    for each released instance.

    Change-Id: Id393d668e0c26c3fc47009f9dc68827618999397
    Closes-bug: #1628905

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/murano 3.1.0 release.