Keystone is experiencing memecached timeouts during tempest tests in
CI, and the memcached log is in excess of 20Mbytes. There will be a lot
of write pressure on this log during tempest tests and this patch reduces
the debug log level in an attempt to increase test reliability.
Change-Id: I7db0eb361fc6f09ce64690be2018bf8ed8204e0c
5080c42f0a