Allow kwargs in _get_router

As a part of the scenario/manager.py stabilization tracked by
the below BP the patch adds kwargs argument for _get_router method
so that the consumers are able to pass additional parameters
if needed.

Implements: blueprint tempest-scenario-manager-stable
Change-Id: I1c6c1a6e0cd5829dd1d497701aad52997f7c5469
1 file changed