Rather than use hard coded auth methods, use the protocal named passed
over the keystone-fid-service-provider relation.
Also, when using federation do not allow the "external" method as they
are mutually exclusive.
Change-Id: I08f0632630d7f0e8d2d7ddb057e02f9febf9ad6f
Closes-Bug: #1828015
Closes-Bug: #1828018