CDRIVER-748 fix mock server for TSAN

mock_server_hangs_up and mock_server_resets were closing a
request stream directly from the main thread. But a request
stream should only be accessed by the worker thread. This
now adds a special reply to the worker thread's queue
to signal a hangup or reset.

Author: kevinAlbs

src/libmongoc/tests/mock_server/mock-server.c

@@ -72,7 +72,9 @@ struct _autoresponder_handle_t {
    int id;
 };
 
-typedef enum { REPLY, HANGUP, RESET } reply_type_t;
+typedef enum {
+   REPLY, HANGUP, RESET
+} reply_type_t;
 
 
 typedef struct {