Add OkHttp driver to support modern HTTP verbs

Add OkHttp driver to support modern HTTP verbs.

Using this driver, all mock and live tests for the OpenStack Marconi API pass, including the ones that use PATCH requests with a body.

This pull requests includes a major refactor of the `BaseHttpCommandExecutorServiceIntegrationTest` class to use mockwebserver and remove the indeterminism introduced by the `BaseJettyTest` class, that made the driver tests fail at random.