Trove should have unit tests isolated from fake-mode int-tests

[Denis M.]

Trove should have unit tests isolated from fake-mode int-tests.
Due to use of common sqllite backend during tox testing unit tests are not failing because sqlite contains required data, such as:
datastore and its versions.

This issue cause next bugs:

 [1] https://bugs.launchpad.net/trove/+bug/1302784
 [2] https://bugs.launchpad.net/trove/+bug/1372950

Steps to fix:

1. Propose method that cleans up backend right after fake-mode int tests are finished. ( the opposite method to util.init_db() )
2. For those tests that are requiring datastore and versions - use common parent class inherited from testtools.TestCase and new class that will hadle datastore registration.

Clarification:

For some reasons (unkonw) int tests attribute was used for unit tests, that why tests at [1] are failing.

https://github.com/openstack/trove/blob/master/trove/tests/unittests/instance/test_instance_status.py#L21

https://github.com/openstack/trove/blob/master/trove/tests/unittests/instance/test_instance_status.py#L36

After further investigation:
17 tests are not isolated and sharing same backend data:

   trove/tests/unittests/backup - 5 usages
   trove/tests/unittests/common - 1 usage (not needed at all)
   trove/tests/unittests/conductor - 1 usage
   trove/tests/unittests/datastore - 1 usage
   trove/tests/unittests/guestagent - 6 usages (which is wrong completely becuase agent is on its way to be moved from codebase)

   trove/tests/unittests/instance - 1 usage
   trove/tests/unittests/mgmt - 1 usage
   trove/tests/unittests/taskmanager - 1 usage

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/125060

[OpenStack Infra (hudson-openstack)]

Change abandoned by Denis M. (<email address hidden>) on branch: master
Review: https://review.openstack.org/125060