Allow optional volumes for nova_libvirt container

Currently there in no heat parameter available to specify optional
volumes for nova_libvirt container.
This patch will allow to attach optional volumes to the nova_libvirt
container through 'NovaLibvirtOptVolumes' heat parameter.

Change-Id: I0651b93fe1e05ca674a3d349a114b980c2005eff
Closes-Bug: #1897265

deployment/nova/nova-libvirt-container-puppet.yaml

@@ -236,6 +236,10 @@ parameters:
       Override the compile time default TLS priority string.
     type: string
     default: 'NORMAL:-VERS-SSL3.0:-VERS-TLS-ALL:+VERS-TLS1.2'
+  NovaLibvirtOptVolumes:
+    default: []
+    description: list of optional volumes to be mounted
+    type: comma_delimited_list
 
 conditions:
 
@@ -708,6 +712,7 @@ outputs:
               list_concat:
                 - {get_attr: [ContainersCommon, volumes]}
                 - {get_attr: [NovaLibvirtLogging, volumes]}
+                - {get_param: NovaLibvirtOptVolumes}
                 -
                   - /etc/ssh/ssh_known_hosts:/etc/ssh/ssh_known_hosts:ro
                   - /var/lib/kolla/config_files/nova_libvirt.json:/var/lib/kolla/config_files/config.json:ro