The ability to run tests at various backend

Added testing functionality for using different db backends. Сurrently
exists ability to define backend-specific tests along with regular
tests. Assuming that the tests will be run under a variety of backend
there exists opportunity to skip backend-specific tests at
inappropriate backends. For the correct functioning of the tests required to
export environment variable with a root access database uri.

Blueprint: tests-given-db-backend
Change-Id: Ic5d3cfe8764b3c04affe79088473255c17535e54