Unittests update

Added _skips_ for tests that require _Phalcon_ or _Fabfuel/Mongo_ extension and moved those two to suggested list in composer.
Most tests base on Interfaces than concrete implementations,  also simplified them in few cases.
Also added usleep() - test were failing when ran on faster machines or without coverage.

The code coverage drops, because you removed the test to check calling stop() without giving a benchmark