* Implement `SaltReturnAssertsMixIn.assertSaltNoneReturn` used in `tests.integration.states.cmd`.
* Migrate `tests.integration.states.cmd` to use `SaltReturnAssertsMixIn`.
Defined "integration.run_tests()" function which can be used to execute
a particular integration test case. Existing bolerplate code in modules
and states tests is replaced with following lines:
if __name__ == '__main__':
from integration import run_tests
run_tests(TestCaseName)
Typical usecase could look like this:
python integration/modules/pip.py --no-clean -vv