support switchover/failover verify empty shell

src/sql/engine/cmd/ob_alter_system_executor.cpp

@@ -1865,6 +1865,8 @@ int ObSwitchTenantExecutor::execute(ObExecContext &ctx, ObSwitchTenantStmt &stmt
 
     // TODO support specify ALL
     if (OB_FAIL(ret)) {
+    } else if (arg.get_is_verify()) {
+      //do nothing
     } else if (OB_FAIL(OB_PRIMARY_STANDBY_SERVICE.switch_tenant(arg))) {
       LOG_WARN("failed to switch_tenant", KR(ret), K(arg));
     }