Release executor jobs on test exit

If a test failed while an executor job was being held, the test
would never exit.  Ensure that all jobs are released during the
shutdown cleanup.

Change-Id: I84d6ffe8aedda3c03ea1cac9b41cfd388f44964b
diff --git a/tests/base.py b/tests/base.py
index e03e6cf..9696c8c 100755
--- a/tests/base.py
+++ b/tests/base.py
@@ -2064,6 +2064,8 @@
 
     def shutdown(self):
         self.log.debug("Shutting down after tests")
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
         self.executor_client.stop()
         self.merge_client.stop()
         self.executor_server.stop()