Correct update URLs (just take them from Bodhi API)
    
    Summary:
    We currently try to figure out the correct URL for updates by
    ourselves, which is finicky and vulnerable to changes in Bodhi.
    For example, right now the URLs are wrong because the Bodhi
    base URL is just 'https://bodhi.fedoraproject.org/' and the
    correct update URL form is '(base_url)updates/(updateid)' but
    we're not including the 'updates/' part, I guess because it
    wasn't needed with the old Bodhi base URL.
    
    Instead of tweaking our URL construction code, let's just throw
    it out and get the update URL from Bodhi now it provides one,
    which should be both easier and safer. I've checked that if you
    use a non-default Bodhi base URL, the API uses that base URL for
    the update's url property - that is, if you run against staging,
    you do get a url that starts with
    'https://bodhi.stg.fedoraproject.org'. So this should be fine.
    
    Test Plan:
    Run a test instance without the fix, try to click on
    an update link, notice it's 404. Run a test instance with the
    fix, try to click on an update link, it should work.
    
    Reviewers: tflink, mkrizek
    
    Reviewed By: mkrizek
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D1050