Allow kwargs in create/restore_backup
Allow kwargs in create/restore_backup

As a part of the scenario/manager.py stabilization tracked by
the below BP the patch adds kwargs argument for create_backup
and restore_backup methods so that the consumers are ableto pass
additional parameters if needed.

Implements: blueprint tempest-scenario-manager-stable
Change-Id: I2ed6eb44bccfdd92ee52d8d1f046ee44308e024d

openstack/tempest,openstack/tempest