set sounds path in here

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@8042 d0543943-73ff-0310-b7d9-9358b9ac24b2

conf/vars.xml

   <!-- Preprocessor Variables
        These are introduced when configuration strings must be consistent across modules. 
    -->
+  <X-PRE-PROCESS cmd="set" data="sound_prefix=$${base_dir}/sounds/en/us/callie"/>
   <X-PRE-PROCESS cmd="set" data="domain=$${local_ip_v4}"/>
   <X-PRE-PROCESS cmd="set" data="moh_uri=local_stream://moh"/>
   <!-- xmpp_client_profile and xmpp_server_profile