Renaming files with savanna words in its names

* Removed etc/savanna directory:
  - all files are moved to etc/sahara
  - updated etc/sahara/compute.topology and etc/sahara/swift.toppology in configs
* Reanmed savannautils.py in HDP plugin
* Renamed savanna_api.py and savanna_db.py, savanna_subprocess.py
  and updated setup.cfg according that
* Modified alembic README since savanna-db-manage entry point changes

Co-Authored-By: Trevor McKay <tmckay@redhat.com>

Change-Id: I67e7abdc9bc68adad401a475095d07a6cef76542
Partial-Implements: blueprint savanna-renaming-service
Merge "Renaming files with savanna words in its names"