nspawn: fix restart-service.yml service list filtering

The service list filtering is supposed to look for all services
that are prefixed with 'service_name', however, we are not doing
that in the regex.

When using nspawn and restarting a service such as 'nova', it matches
the systemd-nspawn service for the container and attempts to reload
it which fails.

This fixes it by forcing it to check for services *prefixed* with
that variable.

Change-Id: Ib1a3975f2722127eada2dd957300fd306abbe6d9

playbooks/common-tasks/restart-service.yml

@@ -23,7 +23,7 @@
 # - service_action: The action to execute [stop, start, restart, reload].
 
 - name: Gather service list
-  shell: "systemctl list-unit-files --state=enabled --type=service | awk '/{{ service_name }}.* enabled$/ {print $1}'"
+  shell: "systemctl list-unit-files --state=enabled --type=service | awk '/^{{ service_name }}.* enabled$/ {print $1}'"
   args:
     executable: "/bin/bash"
   register: _enabled_services