engine: Command for testing provider connectivity

Allows to test that the provider definition allows connecting the
provider and accessing it's API.

Future patches will add the proxy & factory implementations that will
implement this logic.

Change-Id: I19e04f45f72c76f99c283ba39dfa31e3a7624cbf
Signed-off-by: Mike Kolesnik <mkolesni@redhat.com>