get-sp-metadata action hardcodes the location of an sp metadata file
which is incorrect - it should use the application name to allow custom
application names and usage of multiple keystone-saml-mellon
applications (to have multiple IdPs).
In order to make unit testing easier the global variable for the sp
metadata file in actions.py is moved into a function so that it is
evaluated at the function call time, not module import time.
This testing setup gets us 3/4 of the way to a full functional test and
is a step toward a full solution.
The tests will validate Service Provider (SP) metadata and the redirect
relationship between horizon, keystone and the IDP. Samltest.id is used as
the IDP which is currently accessible through our firewalling.
What we are not yet doing is publishing the SP metadata in the IDP and doing
a full login on the IDP.
