don't set key_name if not provided
don't set key_name if not provided

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