1. Fix bug in setting up open-cas in nova-cpu.conf
2. Move volume_local_cache flag to test-config

Change-Id: Ic0684500ed2d5c278629f93ce836a9f34745dad3

This patch updates/adds the contributor documentation to follow
the guidelines of the Ussuri cycle community goal[1].

[1] https://governance.openstack.org/tc/goals/selected/ussuri/project-ptl-and-contrib-docs.html
Story: #2007236
Task: #38554

Change-Id: I66724d6727254ef444612458916df031a694b3f1

Add tempest tests to zuul check and gate. This includes two parts of
tests:
- Tests in tempest repo
- Tests in cinder-tempest-plugin

Change-Id: I6ea4d60f41bf0d312360c450e0038bc6f21a44ce
Signed-off-by: Liang Fang <liang.a.fang@intel.com>

During stack.sh
- git clone open-cas repo
- compile open-cas
- install open-cas
- configure open-cas

During unstack.sh
- remove cached devices
- remove cache instance
- uninstall open-cas

Change-Id: I037b9cf585048b63de6a5f554620a89a8de67e1b
Signed-off-by: Liang Fang <liang.a.fang@intel.com>