Use Tempest-lib's compute server_groups_client

Compute server_groups_client has been migrated to
tempest-lib- Ie95fcbfad5352d272e8977c33f80ebb9769fe824

Now Tempest-lib provides this client as stable interface so Tempest
should start using this from lib and remove its own copy.
Also remove its unit tests.

This commits makes Tempest to use compute server_groups_client
from Tempest-lib.

NOTE- There are difference between migrated files and current tempest file
- I3abac40ebb33836980c119d59bc97f035b213c0a
- I75307176c2f032301da6227249070c42af54dd6e
But those are already taken care in lib.

Change-Id: Ia79db7d9065cad3f21f2bf32b97710438ecaa349
4 files changed