When deployed in a non-ha setup the keystone ip can fail to be
found due to problems with getting ips of subordinates. Also,
there is duplicate code for finding the keystone ip so put this
in the setup class.
SAML Mellon tests have been broken on Focal. The handling of the region
selection behaves differently from bionic. Or it may be that bionic
accidentally was working by seeing a string as int 0.
Horizon has a "default" region which returns the keystone URL.
After a change to the way application name is set and because
keystone-saml-mellon uses BaseKeystoneTest which sets the application
name to "keystone" which breaks KSM actions.
This change explicitly sets application name to keystone-saml-mellon.