Fix leak of SSL caches for auxiliary threads

Whenever a thread creates MySQL connections using SSL params the
thread-local caches are populated. These thread-local resources need to
be free on thread exit via 'mysql_thread_end', otherwise these objects
will be leak. This is not relevant for the fixed size thread-pools, but
it's for workloads making use of temporary/auxiliary threads.

lib/MySQL_Monitor.cpp

@@ -103,7 +103,7 @@ class ConsumerThread : public Thread {
 					m_queue.add(item);
 				}
 				// this is intentional to EXIT immediately
-				return NULL;
+				goto cleanup;
 			}
 
 
@@ -123,6 +123,9 @@ class ConsumerThread : public Thread {
 			delete item->data;
 			delete item;
 		}
+cleanup:
+		// De-initializes per-thread structures. Required in all auxiliary threads using MySQL and SSL.
+		mysql_thread_end();
 		return NULL;
 	}
 };

lib/MySQL_Session.cpp

@@ -329,6 +329,8 @@ __exit_kill_query_thread:
 		delete ssl_params;
 		ssl_params = NULL;
 	}
+	// De-initializes per-thread structures. Required in all auxiliary threads using MySQL and SSL.
+	mysql_thread_end();
 	return NULL;
 }