Avoid hardcoded value in `unicorn_launcher`.

On slower instances, spinning up a new master process
can take more than 10 secs.

config/unicorn_launcher

@@ -15,9 +15,14 @@ function on_reload()
 {
   echo "Reloading unicorn"
   kill -s USR2 $UNICORN_PID
-  sleep 10
+
+  while [ -z "$NEW_UNICORN_PID" ]; do
+    echo "waiting for new unicorn master pid"
+    NEW_UNICORN_PID=`ps -f --ppid $UNICORN_PID | grep 'unicorn master' | grep -v worker | awk '{ print $2 }'`
+    sleep 1
+  done
+
   curl $LOCAL_WEB &> /dev/null
-  NEW_UNICORN_PID=`ps -f --ppid $UNICORN_PID | grep unicorn | grep -v worker | awk '{ print $2 }'`
   kill -s QUIT $UNICORN_PID
   echo "Old pid is: $UNICORN_PID New pid is: $NEW_UNICORN_PID"
   UNICORN_PID=$NEW_UNICORN_PID