wait until the transmission-daemon terminates properly

We should wait for the termination of the transmission-daemon before the s6 service issues a sigterm to all remaining processes.
Without this delay the s6 sigterms are issued right after the RPC 'transmission-remote --exit'. This leaves not time to properly save the settings.json file, stats.json file, all resume files and showing the closing message 'Closing transmission session... done'.

This commit should fix the following issue: https://github.com/linuxserver/docker-transmission/issues/80

root/etc/services.d/transmission/run

@@ -2,11 +2,15 @@
 
 _term() {
   echo "Caught SIGTERM signal!"
+  echo "Tell the transmission session to shut down."
+  pid=$(pidof transmission-daemon)
   if [ ! -z "$USER" ] && [ ! -z "$PASS" ]; then
     /usr/bin/transmission-remote -n "$USER":"$PASS" --exit
   else
     /usr/bin/transmission-remote --exit
   fi
+  # terminate when the transmission-daemon process dies
+  tail --pid=${pid} -f /dev/null
 }
 
         trap _term SIGTERM