nuts: add 20 millisecond delay before nng_fini

This is to allow finalizers to run for the HTTP framework.  This is
a bug workaround for now, and should be fixed in the HTTP framework
later by using reference counts correctly.

src/testing/nuts.h

@@ -23,8 +23,15 @@ extern void nuts_logger(
     nng_log_level, nng_log_facility, const char *, const char *);
 
 // Call nng_fini during test finalization -- this avoids leak warnings.
+// We add a 20 millisecond delay as a hack to allow for other subsytems to
+// drain first. (Notably the HTTP framework can fail if we shut down too
+// quickly.  These bugs should be fixed and then the sleep can be removed.)
 #ifndef TEST_FINI
-#define TEST_FINI nng_fini()
+#define TEST_FINI               \
+	do {                    \
+		nng_msleep(20); \
+		nng_fini();     \
+	} while (0)
 #endif
 
 #ifndef TEST_INIT