Fixups for host/service address variable substitution

Changed HTTP_SERVER_ADDRESS/INTERFACE/PORT to SERVICE_ADDRESS/INTERFACE/PORT.

Changed rygel.conf to have "@SERVICE_ADDRESS@" for the dtcp-host parameter
 in the ODIDMediaEngine config and the MediaEngine code to read the
 configuration as-is - so it can still be explicitly specified via the
 config if/when desired.

Ran the same tests as the previous commits & verified replacement of
 SERVICE_ADDRESS.