Install trousers to get user tss for nova_libvirt

The user tss is wanted by libvirt and comes with the trousers package.
Prior RHEL8 it comes via the gnutls -> trousers dependencies, but there is
no such a dependency in RHEL8, so make sure we have trousers installed.

Change-Id: I9f11ba53d5c6f0a435a62bb462164566c4519d9f
Closes-Bug: #1821309

docker/nova/nova-libvirt/Dockerfile.j2

@@ -19,6 +19,7 @@ LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build
         'libvirt-daemon-driver-lxc',
         'libvirt-daemon-driver-nwfilter',
         'openvswitch',
+        'trousers'
     ] %}
     {% if base_distro in ['centos', 'oraclelinux'] %}
         {% set nova_libvirt_packages = nova_libvirt_packages + [
@@ -41,7 +42,8 @@ LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build
         'pm-utils',
         'qemu-block-extra',
         'qemu-kvm',
-        'qemu-system'
+        'qemu-system',
+        'trousers'
     ] %}
 
     {% if base_arch == "aarch64" %}

releasenotes/notes/add_trousers_to_nova_libvirt-4d159df1079b5c8e.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    The user tss is wanted by libvirt and comes with the trousers package.
+    Prior RHEL8 it comes via the gnutls -> trousers dependencies, but there is
+    no such a dependency in RHEL8, so make sure we have trousers installed.