Change keystone memcache backend

Use keystone memcache pool backend
in order to fix scalability and
failover problems

Also fixing file_line "match" + "after" insertion logic.

Change-Id: Idfe4b54caa0d96a93e93bfff12d8b6216f83e2f1
Closes-bug: #1364401
Closes-bug: #1340657