Fixes for shared memcached to work

* Horizon was not configured properly to use a shared memcached.  It had
  syntax error with config.
* Configured horizon to store sessions into the cache, this is necessary
  for HA horizon.
* Memcached was not configured to listen on it's internal interface, was
  bound to localhost.
* Opened up memcached port for VM testing.
* Proper ownership of /opt/stack/horizon/static/dashboard, which allows
  horizon to create it's css and js dirs.
* The python-memcached module needs added to horizon's venv.