Add several test scripts wrapping test_workqueue

This is a fairly easy way for us to get our test coverage up on
compat_threads.c and workqueue.c -- I already implemented these
tests, so we might as well enable them.

changes/workqueue_tests

@@ -0,0 +1,4 @@
+  o Testing:
+    - Run more workqueue tests as part of "make check". These had previously
+      been implemented, but you needed to know special command-line options
+      to enable them.