Add a way to disable libzmq's internal test timeout.

It's nice to be able to disable libzmq's internal timeout when there's
another timeout in the test runner being used which gives nicer error
messages.

tests/testutil.hpp

@@ -282,8 +282,10 @@ void setup_test_environment()
     // abort test after 121 seconds
     alarm(121);
 #else
+#   if !defined ZMQ_DISABLE_TEST_TIMEOUT
     // abort test after 60 seconds
     alarm(60);
+#   endif
 #endif
 #endif
 #if defined __MVS__