Make freezer-ubuntu as voting job again

freezer-ubuntu job has been made n-v in legacy
job migration work.
- https://review.openstack.org/#/c/642607/

Not issue has been fixed and it is working fine
- https://review.openstack.org/#/c/643213/3

Let's reenable it as voting and running on gate pipeline also.

Story: 2005227
Task: 30009

Change-Id: Ic133fd0d0f37fc65f6dac560644db043ee773904

.zuul.yaml

@@ -10,9 +10,7 @@
       - release-notes-jobs-python3
     check:
       jobs:
-        - freezer-ubuntu:
-            # n-v till story#2005227
-            voting: false
+        - freezer-ubuntu
         - freezer-centos-7:
             voting: false
         - openstack-tox-pylint
@@ -21,8 +19,7 @@
     gate:
       queue: freezer
       jobs:
-        # Commenting as this is n-v job till story#2005227
-        #- freezer-ubuntu
+        - freezer-ubuntu
         - openstack-tox-pylint
         - freezer-tempest-agent
         - freezer-tempest-scheduler