[Delivers #60918200] User update does not work

I've modified the user backend endpoint for updates (POST /users/:id) to allow for both user updates and group assignment.  

To allow for removal of all groups for a repo_id, the "remove_groups" param is required - previously if the "groups" array was empty we would remove groups... but this endpoint is dual purpose and "groups" may be empty/missing if we are just performing a "user" update.

Plus tried to fix some selenium issues.