Minor bug fixed in RO/start_build

Change-Id: I5339ec6d2713de070354eccee56903263fda0d80
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>

jenkins/RO/start_build

@@ -34,7 +34,7 @@ else
 	cd $OSM_MDG
 fi
 if [ $# -gt 0 ]; then
-	git checkout $1
+	git checkout $1 || FATAL "git checkout '$1' didn't work"
 fi
 
 INFO "starting build"