change moh to a var so you can change it with ease

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@6866 d0543943-73ff-0310-b7d9-9358b9ac24b2

conf/dialplan/default.xml

@@ -197,7 +197,7 @@
     <extension name="hold_music">
       <condition field="destination_number" expression="^9999$">
 	<action application="answer"/>
-	<action application="playback" data="local_stream://moh"/>
+	<action application="playback" data="$${moh_uri}"/>
       </condition>
     </extension>