Move code around to group cluster related bits together
Add some internal helpers for clusters
Add helpers for clusters to use in other barclamps
More haproxy work
Fix bugs in WIP
Move DNS synchronization to a different helper

We don't want to do this several times if we have more than one clusters
involved.
Add helpers to get hostnames for OpenStack endpoints

This is common code that all barclamps need, so a helper is a good
thing.
Merge pull request #15 from vuntz/haproxy

[WIP] HA with HAProxy