nailgun-agent: use service command to restart mcollective

mcollectived can be launched via upstart job or systemd unit.
Fortunately the service command hides those gory details.

Change-Id: Iad4c8bc5d89176513b4d3bcc37a4161a9d900caf
Related-Bug: #1454741

agent

@@ -109,11 +109,7 @@ class McollectiveConfig
         @logger.info "Identity in mcollective server.cfg has not been found. Setting to '#{new_id}'"
         File.open(@configfile, "w") { |f| f.write(config) }
       end
-      # Generally because generic init script for
-      # mcollective is broken at least in Ubuntu and
-      # altering restart in such way seems better
-      # than shipping our own package.
-      puts `/etc/init.d/mcollective stop; /etc/init.d/mcollective start`
+      puts `service mcollective restart`
     end
   end
 end