Support classes for heat integration tests

These support classes started as a forklift of the classes needed
to run tempest scenario orchestration tests.

The original tempest code has been pared back to provide the
small subset required by heat integration tests. From this point on
these support classes can evolve to the specific needs of the
integration tests.

There is some unused code (especially in remote_client) which has
been left in as it may become useful in the future, and is already
extremely well reviewed and tested from being developed for tempest.

The script heat_integrationtests/generate_sample.sh will generate
an up-to-date heat_integrationtests/heat_integrationtests.conf.sample
file which can be copied to
heat_integrationtests/heat_integrationtests.conf
to override default configuration values. A local ConfigOpts is created
for each test to avoid any potential interaction with heat's
global CONF. Configuration options for credentials default to
being sourced from the environment.

The default tox testenv now excludes tests in heat_integrationtests.
A new testenv called "integration" will only run tests in
heat_integrationtests.

Integration tests will fail if preconditions are not met, including
a keystone endpoint, credentials and glance containing the expected
named image.

Devstack gate hooks have been moved to heat_integrationtests now that
the name of the package has been decided.

Change-Id: I174429c16bb606c5c325ee8b62c6e600ea77a6e6
Partial-Blueprint: functional-tests
Merge "Support classes for heat integration tests"