Switch to local copy of scenario test base class

This is in response to the mailing list post at:
http://lists.openstack.org/pipermail/openstack-dev/2017-February/112938.html

The tempest.scenario.manager class will be refactored,
so a local copy will be maintained in the
barbican_tempest_plugin repository until that refactor
is complete.

Change-Id: I706e256fe4e224e44532ea0ce2c81495791ec97f
2 files changed