Deprecate Tempest stress tests

As discussed on ML [1], we should have Tempest
more towards it core mission and stress tests framework
is one which does not fit much here.

This commit adds deprecation warning for the Stress tests.

Those will be removed in Newton.

1- http://lists.openstack.org/pipermail/openstack-dev/2016-February/086336.html

Change-Id: I41b42e02ff17f2d98862ddb11f137580abadafde
2 files changed