Public IP for gateway, checkin chefserver (all VMs), and periodic poll

* chefserver can checkin (knife bootstrap) itself

* add floating ip to gateway

* periodic poll to check whether all servers are up
* print all exceptions in cleanup()

* add SshConnectionError, and catch more specific exceptions in
  polling
Merge pull request #14 from changbl/working

Public IP for gateway, checkin chefserver (all VMs), and periodic poll