Use a reliable failure mechanism in test enclosure

`assert(false)` gets compiled out in release build unit tests, which prevents this case from properly generating a user warning.  Switching `assert(false)` with the googletest macro `ASSERT_TRUE()` provides more reliability and the added benefit of debug text.

autowiring/AutowiringEnclosure.h

@@ -103,10 +103,7 @@ class AutowiringEnclosure:
     ctxt->SignalShutdown();
 
     // Do not allow teardown to take more than 250 milliseconds or so
-    if(!ctxt->Wait(std::chrono::milliseconds(250))) {
-      // Critical error--took too long to tear down
-      assert(false);
-    }
+    ASSERT_TRUE(!ctxt->Wait(std::chrono::milliseconds(250))) << "Test case took too long to tear down, unit tests running after this point are untrustworthy";
 
     static const char sc_autothrow [] = "AUTOTHROW_";
     if(!strncmp(sc_autothrow, info.name(), sizeof(sc_autothrow) - 1))