Test checks that create/delete stacks actions are executed without
errors under admin user.
Stacks page object was defined similar to other pages.
Few other modifications I've made:
* horizon.conf - service_available section with new heat option
* stack template is added as separate file
Depends-On: I1f5dc1220aee39103289a579583095346cce0354
Implements blueprint: horizon-integration-tests-coverage
Change-Id: Ibc549f9ae4eac17d8e92d65afe1c5cee9be6e72e
This will allow us to modify devstack environment of a
dsvm-integration job independently of infra repository, once
https://review.openstack.org/#/c/269578/ is merged. This is a
preparation to integration testing of Heat-enabled panel in Horizon,
since Heat is disabled in Devstack by default.
Change-Id: Id9ab8e846c33921e1c55e459056345c8d14204fd