docs: fix quoting issue, clarify naming in auth.md (#931)
docs: fix quoting issue, clarify naming in auth.md (#931)

The steps for creating serving certificates were missing a pair of
quotes, which could have lead to some confusion.

This also clarifies the naming of the serving certs a bit: many places
refer to the cert and key as `.crt` and `.key`, but `cfssl` outputs them
as `.pem` and `-key.pem`.
kubernetes-sigs/service-catalog,arschles/kubernetes-service-catalog,staebler/service-catalog,arschles/kubernetes-service-catalog,krancour/service-catalog,jboyd01/service-catalog,MHBauer/service-catalog,duglin/service-catalog,kubernetes-sigs/service-catalog,MHBauer/service-catalog,staebler/service-catalog,n3wscott/service-catalog,MHBauer/service-catalog,MHBauer/service-catalog,duglin/service-catalog,duglin/service-catalog,n3wscott/service-catalog,martinmaly/service-catalog,kibbles-n-bytes/service-catalog,duglin/service-catalog,vaikas-google/service-catalog,vaikas-google/service-catalog,jboyd01/service-catalog,pmorie/service-catalog,MHBauer/service-catalog,martinmaly/service-catalog,kubernetes-sigs/service-catalog,pmorie/service-catalog,kubernetes-incubator/service-catalog,duglin/service-catalog,n3wscott/service-catalog,n3wscott/service-catalog,staebler/service-catalog,mdshuai/service-catalog,kubernetes-incubator/service-catalog,duglin/service-catalog,krancour/service-catalog,staebler/service-catalog,jboyd01/service-catalog,mdshuai/service-catalog,kibbles-n-bytes/service-catalog,kibbles-n-bytes/service-catalog,arschles/kubernetes-service-catalog,staebler/service-catalog,kibbles-n-bytes/service-catalog,pmorie/service-catalog,jboyd01/service-catalog,mdshuai/service-catalog,n3wscott/service-catalog,jboyd01/service-catalog,MHBauer/service-catalog,n3wscott/service-catalog,jboyd01/service-catalog,krancour/service-catalog,vaikas-google/service-catalog,martinmaly/service-catalog,kubernetes-sigs/service-catalog,kubernetes-sigs/service-catalog,kibbles-n-bytes/service-catalog,kibbles-n-bytes/service-catalog,kubernetes-incubator/service-catalog,staebler/service-catalog,kubernetes-incubator/service-catalog,kubernetes-incubator/service-catalog,kubernetes-incubator/service-catalog,kubernetes-sigs/service-catalog