Several executor threading fixes

* Add a try/except handler to the governor thread
* Add names to all executor threads
* Show thread names in the stack dump handler

Change-Id: I7551a901ffba175224d417f653391c4568f9975b
diff --git a/tests/unit/test_stack_dump.py b/tests/unit/test_stack_dump.py
index 824e04c..13e83c6 100644
--- a/tests/unit/test_stack_dump.py
+++ b/tests/unit/test_stack_dump.py
@@ -31,4 +31,5 @@
 
         zuul.cmd.stack_dump_handler(signal.SIGUSR2, None)
         self.assertIn("Thread", self.log_fixture.output)
+        self.assertIn("MainThread", self.log_fixture.output)
         self.assertIn("test_stack_dump_logs", self.log_fixture.output)