Use Queens UCA for nova-multiattach job

The dependent change to devstack makes devstack use the
Queens Ubuntu Cloud Archive which has libvirt 4.0.0 so we
can remove the flag from the job which disabled the UCA
in devstack since the versions of qemu and libvirt in the
Pike UCA wouldn't work for multiattach.

This also allows us to make the job voting and gating again.

Closes-Bug: #1763382

Depends-On: https://review.openstack.org/554314
Depends-On: https://review.openstack.org/560931
Change-Id: I0962474ff6dfc5fa97670c09a1af97a0f34cd54f

.zuul.yaml

@@ -92,14 +92,9 @@
       Run tempest integration tests with volume multiattach support enabled.
       This job will only work starting with Queens.
       It uses the default Cinder volume type in devstack (lvm) and the
-      default compute driver in devstack (libvirt). It also disables the
-      Pike Ubuntu Cloud Archive because volume multiattach support with
-      the libvirt driver only works with qemu<2.10 or libvirt>=3.10 which
-      won't work with the Pike UCA.
+      default compute driver in devstack (libvirt).
     run: playbooks/legacy/nova-multiattach/run.yaml
     post-run: playbooks/legacy/nova-multiattach/post.yaml
-    # TODO(mriedem): Make this job voting and gating once bug 1763382 is fixed.
-    voting: false
 
 - job:
     name: nova-next
@@ -127,6 +122,7 @@
     gate:
       jobs:
         - nova-cells-v1
+        - nova-multiattach
         - nova-next
         - nova-tox-functional
         - nova-tox-functional-py35