Embed the ProviderClient struct in ServiceClient.
Embed the ProviderClient struct in ServiceClient.

This lets us inherit the AuthenticatedHeaders method, rather than
having to walk the references all the time.

jamiehannaford/gophercloud,sti-jans/gophercloud,jarosser06/gophercloud,clintonskitson/gophercloud,feiskyer/gophercloud,feiskyer/gophercloud,pratikmallya/gophercloud,carolynvs/gophercloud,timbyr/gophercloud,rackspace/gophercloud,carolynvs/gophercloud,rgbkrk/gophercloud,rgbkrk/gophercloud,larsbutler/gophercloud,trumant/gophercloud,trumant/gophercloud,jarosser06/gophercloud,clintonskitson/gophercloud,rackspace/gophercloud,timbyr/gophercloud,DSpeichert/gophercloud,DSpeichert/gophercloud,dudymas/gophercloud,pratikmallya/gophercloud,larsbutler/gophercloud,dudymas/gophercloud,jamiehannaford/gophercloud,sti-jans/gophercloud