MINOR: exec pebble to be a PID 1 process

Author: hdurand0710

fs/start-pebble.sh

@@ -21,4 +21,4 @@ if [ ! -e /etc/haproxy/haproxy-aux.cfg ]; then
 fi
 
 export EXTRA_OPTIONS="$@"
-pebble run --verbose
+exec pebble run --verbose