setup.sh: Exit on first test failure.

This was the intent of "false" with "set -eu", but did not work.
diff --git a/setup.sh b/setup.sh
index 214bcfd..18a492c 100755
--- a/setup.sh
+++ b/setup.sh
@@ -6,7 +6,7 @@
     :
   else
     echo "runTestLibusb.sh failed with ${python_v} ($("$python_v" --version))"
-    false
+    exit 1
   fi
 done
 export I_KNOW_HOW_TO_RELEASE_PYTHON_LIBUSB1=1