Lots of cleanups to self-tests

* Removed or truncated sleeps so the tests run faster
* Removed dependencies on zmq_utils
* Rewrote a few tests that were confusing
* Minor code cleanups

tests/test_reqrep_ipc.cpp

@@ -23,8 +23,6 @@
 
 int main (void)
 {
-    fprintf (stderr, "test_reqrep_ipc running...\n");
-
     void *ctx = zmq_ctx_new ();
     assert (ctx);