Eliminate jobset timeouts in some circumstances

There are cases where we truly don't care how long something takes, and
some external timeout will kill truly stuck processes, so let's
eliminate timeouts in those cases
diff --git a/tools/run_tests/jobset.py b/tools/run_tests/jobset.py
index e33433d..748c06d 100755
--- a/tools/run_tests/jobset.py
+++ b/tools/run_tests/jobset.py
@@ -273,7 +273,9 @@
         self.result.state = 'PASSED'
         if self._bin_hash:
           update_cache.finished(self._spec.identity(), self._bin_hash)
-    elif self._state == _RUNNING and time.time() - self._start > self._spec.timeout_seconds:
+    elif (self._state == _RUNNING and 
+          self._spec.timeout_seconds is not None and 
+          time.time() - self._start > self._spec.timeout_seconds):
       if self._timeout_retries < self._spec.timeout_retries:
         message('TIMEOUT_FLAKE', '%s [pid=%d]' % (self._spec.shortname, self._process.pid), stdout(), do_newline=True)
         self._timeout_retries += 1