Resolves Horizon and Nova-Compute key distribution issues

Horizon and Nova-Compute had several outstanding issues regarding the distribution of keys throughout the cluster. The issues were mainly access problems when connecting to localhost and a potential issue with temp files being saved on the deployment host which contained ssh and ssl keys. To resolve both issues temporary objects can now be securely stored in memcached using the ansible memcached module. The module allows objects to be AES encrypted using the same memcached key already being set for use within the cluster. Additionally, the temporary objects are set to expire after 300 seconds. See the module for more details and documentation. 

Related Issues:
* https://github.com/rcbops/ansible-lxc-rpc/issues/62
* https://github.com/rcbops/ansible-lxc-rpc/issues/74

Related Pending Workarounds:
* https://github.com/rcbops/ansible-lxc-rpc/pull/91

The Horizon playbook was updated to remove all of the misc installation things being done, which were mostly leftover from when the play was original created. The play is now being called and installed like all the other plays in the stack; options have been segmented out, the one-off package building for horizon is now integrated into the container's system resources, and all of the SSL certs are sync'd to all horizon nodes. 

Horizon is now using a SHA as the git branch and was done to to being resolving Issue: https://github.com/rcbops/ansible-lxc-rpc/issues/31

This should no longer be an issue. The horizon host group was removed from openstack_common because the vars were moved and horizon has it's own common play.