Overwrite hostname reported by ganglia

User ganglia's overwrite_hostname to force the VM hostname. Avoids VMs
on private networks to appear as their gateway in the ganglia monitoring
interface. Requires ganglia puppet module at commit
MadMalcolm/puppet-ganglia@7e0c34f6e5397f5b49e01a832ac3741c90c13c2a.
Added group ssh keys for debugging access.

Changes:
	modified:   manifests/site.pp
	modified:   modules/gce_node/manifests/init.pp