Add a servers context and a cinder stress scenario

Based on https://github.com/WaltHP/cinder-stress/commits/master/qaStressTest.py
this scenario creates n volumes and performs the following sequence using
those volumes:

1. Create snapshots
2. Attach volumes
3. Detach volumes
4. Delete snapshots
5. Delete volumes

The servers context setup instantiates n servers and removes them on cleanup.

Co-Authored-By: Cesar Mojica <cesar.mojica@hp.com>
Co-Authored-By: Anthony Lee <anthony.mic.lee@hp.com>
Change-Id: I8e32cbef57f12079e78a8f7ae73f2af4835d2cb5
Merge "Add a servers context and a cinder stress scenario"