Not deterministic failure in service_update_test_stack_preview

[Steven Hardy]

Running the unit tests locally I'm sometimes seeing this:

pythonlogging:'': {{{INFO [heat.engine.service] Previewing update of stack service_update_test_stack_preview}}}

Traceback (most recent call last):
  File "heat/tests/engine/service/test_stack_update.py", line 748, in test_stack_update_preview_replaced_update_not_allowed_prop
    replaced = [x for x in result['replaced']][0]
IndexError: list index out of range
Ran 5121 (+2) tests in 405.847s (-15.909s)
FAILED (id=63, failures=1 (+1), skips=6)
error: testr failed (1)
ERROR: InvocationError: '/opt/stack/heat/.tox/py27/bin/python setup.py testr --slowest --testr-args=^(?!heat_integrationtests)'
_________________________________________________________________ summary _________________________________________________________________
ERROR: py27: commands failed

Then, running tox -e py27 again works. Not sure of the root cause yet, but clearly it's not good if this is also happening in the gate.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/224964

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/224964
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=bab3b3afaaee5973177e16cfc01ee8384eee34ec
Submitter: Jenkins
Branch: master

commit bab3b3afaaee5973177e16cfc01ee8384eee34ec
Author: Steve Baker <email address hidden>
Date: Fri Sep 18 02:28:11 2015 +0000

    Revert "Additional unit tests for update-preview"

    Both of these tests appear to have races which cause gate
    failures. This is affecting RC1 changes landing so lets
    revert for now while it is investigated.

    This reverts commit 92107789ad28da86b877e1d0c35cb0c7a8e9e437.
    Closes-Bug: #1496886

    Change-Id: I411be70ab88e05ad9dc79b3bf147b282bbda34b0