Changes frozen repo to point to mirror.rackspace.com

The rpc-slushee.rackspace.com has numerous issues, so
we have created mirror.rackspace.com/rackspaceprivatecloud
to address those issues.  All instances of rpc-slushee
have been replaced.

Backported for proposed/juno
Fixes #527

(cherry picked from commit 95770070b25ea3eddf31fcf48ed510ef1f6badcf)

Conflicts:
	rpc_deployment/inventory/group_vars/all.yml