Use older keepalived version in functional tests

It looks that current keepalived version which is available in
Ubuntu Xenial repositories (1:1.2.24-1ubuntu0.16.04.1) is broken
and cause failure of some functional tests in Neutron.
Details are in [1].
Older version works fine so as temporary solution we can use
this version in functional tests.

This issue don't happens on master and stable/rocky branch, as there
newer cloud-archive repo is used and it has newer version of keepalived
which works fine.

[1] https://bugs.launchpad.net/ubuntu/+source/keepalived/+bug/1789045

Change-Id: I418a967cd503991736e72134d4a105b6e97021e8
Closes-Bug: #1788185

neutron/tests/contrib/gate_hook.sh

@@ -82,6 +82,13 @@ case $VENV in
         # See commit 138df3e563de9da0e5a4155b3534a69621495742 (on the ovs repo).
         OVS_BRANCH="138df3e563de9da0e5a4155b3534a69621495742"
         compile_ovs_kernel_module
+    elif [[ "$VENV" =~ "dsvm-functional" ]]; then
+        # NOTE(slaweq): there is some bug in keepalived
+        # 1:1.2.24-1ubuntu0.16.04.1, and because of that we have to use older
+        # version for tests as workaround. For details check
+        # https://bugs.launchpad.net/neutron/+bug/1788185
+        # https://bugs.launchpad.net/ubuntu/+source/keepalived/+bug/1789045
+        sudo apt-get install -y --allow-downgrades keepalived=1:1.2.19-1
     fi
 
     # prepare base environment for ./stack.sh