Allow for REMOTE_USER name in federation mapping

Co-Authored-By: Marek Denis <marek.denis@cern.ch>

Change-Id: I74e2599394752c75a0df3090c74f7b5c54c771e0
Closes-Bug: #1390085
Don't return ``user_name`` in mapped.Mapped class.

auth.mapped.Mapped._handle_unscoped_token() and _setup_username don't
need to return and store variable ``user_name``. Drop it.

Change-Id: Id66e63a49a146a04217ad5c548cd877819aa9ca2
Move test_pemutils.py to unit test directory

The test_pemutils.py module consists of unit tests for common Keystone
code. This commit moves the test_pemutils.py unit tests to the
keystone/tests/unit/common directory.

Change-Id: Ifeedaaf2fb7cd379bb9e872567874bced0c94b02
Merge "Move test_pemutils.py to unit test directory"
Merge "Allow for REMOTE_USER name in federation mapping"
Merge "Don't return ``user_name`` in mapped.Mapped class."