Update memcache backend

Update memcache client depending on the openstack
release. From Ocata and older use new client PyLibMCCache,
because MemcachedCache stop maintaining in upstream.

Change-Id: Ib49bb3b4b8e312615cf9ccfcbe4fb4aa4c37e4c8
Related-Prod: PROD-19810 (PROD:19810)
2 files changed