Order imports in alphabetical order (4/9)

This patch is one in a series to re-enable H306 style check rule
(imports are in alphabetical order). It touches db files.

Implements: blueprint reduce-flake8-ignored-rules (partial)
Change-Id: I66842c6a5d112f948e625e18ef6d01afcad61e57
Remove unused code in test_validate.py

Remove the mock of instances.Instance.nova() for some tests.

Change-Id: I48aaaacaa827cd96ad2372011daf48e386e87c01
Run pep8 check in run_tests.sh as in tox

Until now the flake8 tests run by tox and run_tests.sh were a bit
different - run_tests.sh was not checking heat-* python scripts in bin
folder and was checking the docs folder that is ignored in tox' pep8
check.

This patch brings pep8 style checking done by run_tests.sh in line with
what is done by tox (and thus the gate).

Change-Id: Ie3f2c25210075df6b941854737f0d926d141601b
Credentials for native heat os-collect-config polling

For Server software_config_transport=POLL_SERVER_HEAT the os-collect-config
configuration has been changed in the following way:
* included stack_id and resource_name
* replaced username with user_id, since domain users should always be
  referenced by ID.
* renamed the collector key from "heat_server_poll" to "heat" since that
  is the intended name for the heat collector in os-collect-config

Closes-Bug: #1299986

Change-Id: I42326c81c7276d7d305a05c00d72a6102e80abca
Merge "Order imports in alphabetical order (4/9)"
Merge "Credentials for native heat os-collect-config polling"
Merge "Remove unused code in test_validate.py"
Merge "Run pep8 check in run_tests.sh as in tox"