Enforce authenticated=False in saml2 plugin

All underlying HTTP calls executed via ``keystoneclient.session.Session``
object should have ``authenticated=False`` option enforced indicating the
plugin is not authenticated with the Identity Service yet.

Change-Id: I946f1ed6a55c4172d8f4bf6a24e5cbc3a00d1154
Rename saml2_token_url to token_url

For the consisteny a property returning authentication url
should be called token_url.
This patch renames ``saml2_token_url`` to ``token_url`` in the
contrib.auth.v3.saml2.Saml2UnscopedPlugin plugin.

Change-Id: I435a118bb31338a37a29eec68b8e9ce50d163675
Insert space between ``#`` and the comment

test_auth_saml2.py file has a comment:
 ``#for better readibility``. A space should be inserted between
 a ``#`` and the comment message.

Change-Id: Ic36bf9254beee9a3f6f1fa904184c17a28f4fa13
Merge "Insert space between ``#`` and the comment"
Merge "Enforce authenticated=False in saml2 plugin"
Merge "Rename saml2_token_url to token_url"
Test commit