This commit adds installing and configuring memcached to the api
server. It then configures the api server to use memcached for it's
local response cache. This is needed to enable the async worker from
openstack-health change I0fd29839c72ca2fdfb4c4724bb3da7e283e3d27d.
Change-Id: I3057e7f9f920550a12c12c1bfeb643a713c5f696
814b6585e5