add loop_until_fail helper (#31360)

* helper

* remove count
old-commit-hash: 2e7ed5bd88

selfdrive/test/loop_until_fail.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -e
+
+# Loop something forever until it fails, for verifying new tests
+
+while true; do
+  $@
+done