Allow kwargs in get_timestamp
Allow kwargs in get_timestamp

As a part of the scenario/manager.py stabilization tracked by
the below BP the patch adds kwargs argument to support
username parameter of get_remote_client() method.

Change-Id: I8e0da8b19b2b0b147b36c392fa4e161115325cd7
Implements: blueprint tempest-scenario-manager-stable

openstack/tempest,openstack/tempest