Need to have stable tempest scenario manager

This patch addresses following facts:
1. common manager methods among plugins should be
   defined in Tempest.
2. methods should be consistent with names and
   parameters.
3. Add docstring about method usage and parameter.

Implements: blueprint tempest-scenario-manager-stable
Signed-off by: Soniya Vyas<svyas@redhat.com>
Change-Id: I191c8861c9ec29b78c9c8ad12ff2ddf3ffbf4db1
3 files changed