Debian: use Ussuri binary packages

There is a repo with binary packages for Ussuri. Let us use them instead
of Train ones.

amd64 only

Change-Id: I071eebc4f60094d881a68e201e8c3bb6e6742ff5

docker/base/Dockerfile.j2

@@ -377,7 +377,7 @@ COPY apt_preferences /etc/apt/preferences.d/kolla-custom
     {% set remote_apt_keys = [
       'https://download.docker.com/linux/debian/gpg',
       'https://packages.grafana.com/gpg.key',
-      'http://buster-train.debian.net/debian/dists/pubkey.gpg',
+      'http://buster-ussuri.debian.net/debian/dists/pubkey.gpg',
       'https://packages.treasuredata.com/GPG-KEY-td-agent',
       'https://repos.influxdata.com/influxdb.key',
       'https://obs.linaro.org/repos/home:/marcin.juszkiewicz/debian-buster/Release.key',

docker/base/apt_preferences.debian

@@ -36,3 +36,8 @@ Pin-Priority: 700
 Package: *libvirt*
 Pin: release o=Debian,b=ppc64le
 Pin-Priority: 700
+
+# ovn-host depends on openvswitch from buster
+Package: openvswitch*
+Pin: release n=buster
+Pin-Priority: 700

docker/base/sources.list.debian

@@ -7,9 +7,9 @@ deb http://security.debian.org/debian-security buster/updates main
 # debian backports
 deb http://deb.debian.org/debian buster-backports main
 
-# Buster - Train repos
-deb http://buster-train.debian.net/debian buster-train-backports main
-deb http://buster-train.debian.net/debian buster-train-backports-nochange main
+# Buster - Ussuri repos
+deb http://buster-ussuri.debian.net/debian buster-ussuri-backports main
+deb http://buster-ussuri.debian.net/debian buster-ussuri-backports-nochange main
 
 # NOTE(hrw): repositories below are added into image when they are needed as
 # separate files in /etc/apt/sources.list.d/ directory. For that purpose they