Rename the jsonresults files for the old "GTK Linux 64-bit Release" bot
Fetch the jsonresults for the old bot "GTK Linux 64-bit Release WK2 (Tests)".
Fetch up to r168841 for the actual bot "GTK Linux 64-bit Release (Tests)".
Add support for getting and mixing the results for more than one bot:

  * Get and parse the results for the 3 GTK release bots:
    * "GTK Linux 64-bit Release (Tests)" is the current GTK release bot
      (since r168495).
    * The other two: "GTK Linux 64-bit Release" and
      "GTK Linux 64-bit Release WK2 (Tests)" were the older names for
      the GTK release bot.
      We use them to get info for older revisions.