Turn on FT voting

Finally FT failures, many of which were due to bugs in FT codebase
itself, have been eliminated [1].

[1]: one non-deterministic failure remains at
test_vnf_alarm_scale_with_instance_reservation.
It's likely that "blazar host-create" fail for all hypervisors due to
timing issue (i.e., >0 instances runnning on all hosts), in which case
we expect "skipTest" to be triggered. However, sometimes it fails to be
done so correctly just returning "FAILED", even though the subsequent
test code seemed not to run at all. If you run into it, just "recheck".
If you figure out the root cause, please push a commit.

Change-Id: Ibcae265b39200ae4b605b00398e3e3e881ef3886

.zuul.yaml

@@ -176,5 +176,4 @@
       - release-notes-jobs-python3
     check:
       jobs:
-        - tacker-functional-devstack-multinode-python3:
-            voting: false
+        - tacker-functional-devstack-multinode-python3