createhdds: flip updates_img image over to new updates image

Summary:
this goes with D799, which changes the updates image tests to
use a different updates image that works with current anaconda.
One of the updates image tests is for loading the updates image
from a hard disk, so we have a hard disk image that contains
the updates image, so that needs rebuilding with the new update
image. Simples! This is the first time we use 'imgver', I knew
it'd come in handy some time...

Test Plan:
Apply with D799, do `createhdds.py all --clean`, make
sure the new image is built and the old one removed, run the
tests and make sure they work (especially install_updates_img_
local).

Reviewers: jskladan, garretraziel

Reviewed By: garretraziel

Subscribers: tflink

Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D800

hdds.json

@@ -73,6 +73,7 @@
         {
             "name" : "updates_img",
             "size" : "100M",
+            "imgver" : "2",
             "parts" : [
                 {
                     "filesystem" : "ext4",
@@ -86,7 +87,7 @@
                 {
                     "part" : "1",
                     "target" : "/updates.img",
-                    "source" : "https://fedorapeople.org/groups/qa/updates/updates-unipony.img"
+                    "source" : "https://fedorapeople.org/groups/qa/updates/updates-openqa.img"
                 }
             ]
         },