MDEV-10564: Galera `wsrep_debug` patch logs MySQL user credentials

Restricted output for CREATE USER, GRANT, REVOKE and SET PASSWORD
so that it shows only above keywords but not rest of query i.e.
not user or password.

sql/wsrep_mysqld.cc

@@ -1450,6 +1450,25 @@ static bool wsrep_can_run_in_toi(THD *thd, const char *db, const char *table,
   }
 }
 
+static const char* wsrep_get_query_or_msg(const THD* thd)
+{
+  switch(thd->lex->sql_command)
+  {
+    case SQLCOM_CREATE_USER:
+      return "CREATE USER";
+    case SQLCOM_GRANT:
+      return "GRANT";
+    case SQLCOM_REVOKE:
+      return "REVOKE";
+    case SQLCOM_SET_OPTION:
+      if (thd->lex->definer)
+	return "SET PASSWORD";
+      /* fallthrough */
+    default:
+      return thd->query();
+   }
+}
+
 /*
   returns: 
    0: statement was replicated as TOI
@@ -1472,7 +1491,8 @@ static int wsrep_TOI_begin(THD *thd, char *db_, char *table_,
   }
 
   WSREP_DEBUG("TO BEGIN: %lld, %d : %s", (long long)wsrep_thd_trx_seqno(thd),
-              thd->wsrep_exec_mode, thd->query() );
+              thd->wsrep_exec_mode, wsrep_get_query_or_msg(thd));
+
   switch (thd->lex->sql_command)
   {
   case SQLCOM_CREATE_VIEW:
@@ -1546,8 +1566,8 @@ static void wsrep_TOI_end(THD *thd) {
   wsrep_status_t ret;
   wsrep_to_isolation--;
 
-  WSREP_DEBUG("TO END: %lld, %d : %s", (long long)wsrep_thd_trx_seqno(thd),
-              thd->wsrep_exec_mode, (thd->query()) ? thd->query() : "void");
+  WSREP_DEBUG("TO END: %lld, %d: %s", (long long)wsrep_thd_trx_seqno(thd),
+              thd->wsrep_exec_mode, wsrep_get_query_or_msg(thd));
 
   wsrep_set_SE_checkpoint(thd->wsrep_trx_meta.gtid.uuid,
                           thd->wsrep_trx_meta.gtid.seqno);