Adding test for cohort uploading for cohort with cyrilic and arabic usernames.

Added ability to specify an arbitrary cohort file and test that it validates correctly.

In order to have testing bindings in mediawiki testing db create tables that
mimic production as close as possible, changes were done to mediawiki user model
and wikimetrics database. Alembic migration is included.
Without the database and binding changes the cohort uploading tests will fail.

Much testing was done regarding database connection args and encoding in
both wikimetrics and mediwiki database on staging with real data.

Bug: 63933
Change-Id: I0771e74f3d0745737e3ea96482614382fe09d961