Refactoring cinder support

* Change execute_command error handling

Change-Id: I6f4da62ce8e0ed517a3ef0d6fa55aa3d77f06c3a
Limit requests version

Add <1.2.3 constraint to the requests version to avoid problems with old
versions of python clients. This constraint could be removed when all
clients will be released w/o such constraint and os/reqs will be updated
to support at least such versions of clients.

Change-Id: I3018357a6ac3f1cc7809bd091ec84aa11b83bf0c
Merge "Limit requests version"
Merge "Refactoring cinder support"