Parsing paths incorrect for discovery service

[alanbarrett]

1. The regular expression to match a discovery_response endpoint should ignore the entityID query string which will be different each time. (so the match should not be to the end of the line.)

2. context.path is the correct query string to use to extract the entityID. context.request is empty.

https://github.com/IdentityPython/SATOSA/blob/master/tests/satosa/backends/test_saml2.py#L118 makes the assumption that context.request is where the query string should be. My tests on a live system show otherwise.

Relevant spec is here and it indicates a GET should be used... http://docs.oasis-open.org/security/saml/Post2.0/sstc-saml-idp-discovery.pdf

3. However, in some implementations context.request seems to contain "entityID", so that also needs to be supported.