test-distro: Fix broken help case statement

Change-Id: I29d20b200162511fd8dd5d577df57b3f3fd680a9
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/test-distro.sh b/test-distro.sh
index c6a5f21..17f40b8 100755
--- a/test-distro.sh
+++ b/test-distro.sh
@@ -62,7 +62,8 @@
       echo build and test the repositories described in config.xml. Individual
       echo repositories can be tested against DOCKERBASE with the --repository
       echo option \(in place of --config\).
-
+      exit 0
+      ;;
     *)
       (>&2 echo Unrecognised argument \'$1\')
       shift