add api fqdn to chef-server.rb and frontend hosts files

* add hostsfile cookbook as dependency 
* store pivotal.pem in "stash" - needed on frontends to run pedant
* add hostfile entry on frontends for api fqdns. alias includes api_fqdn setting in topology data bag
* add api_fqdn to chef-server.rb (from api_fqdn setting topology data bag )

converged and could run chef-server-ctl test successfully

@jtimberman @paulmooring 
Why is an /etc/hosts entry needed? Perhaps instead of hostnames we should be using IP addresses, except in the case of VIPs, which isn't supported yet?

I'd rather not add this resource/cookbook, especially in a default use context, as it makes the assumption we're not using proper DNS entries, and adds a layer of complex indirection that makes it more difficult to reason about.