Make rocksdb.read_only_tx pass and enable it

- FB/MySQL 5.6' MyRocks has START TRANSACTION WITH CONSISTENT
  ROCKSDB SNAPSHOT, which returns binlog position.

- MariaDB has a cross-engine START TRANSACTION WITH CONSISTENT
  SNAPSHOT. It can be used for the same purpose. Binlog position
  can be obtained from Binlog_snapshot_file/position status vars.

storage/rocksdb/mysql-test/rocksdb/r/read_only_tx.result

 DROP TABLE IF EXISTS t1;
+connect  con1,localhost,root,,;
+connect  con2,localhost,root,,;
+connection con1;
 CREATE TABLE t1 (id INT, value int, PRIMARY KEY (id), INDEX (value)) ENGINE=RocksDB;
 INSERT INTO t1 VALUES (1,1);
 select variable_value into @p from information_schema.global_status where variable_name='rocksdb_number_sst_entry_put';
 select variable_value into @s from information_schema.global_status where variable_name='rocksdb_number_sst_entry_singledelete';
-START TRANSACTION WITH CONSISTENT ROCKSDB SNAPSHOT;
-File	Position	Gtid_executed
-master-bin.000001	734	uuid:1-3
+START TRANSACTION WITH CONSISTENT SNAPSHOT;
+connection con2;
+connection con1;
 select case when variable_value-@p < 1000 then 'true' else variable_value-@p end from information_schema.global_status where variable_name='rocksdb_number_sst_entry_put';
 case when variable_value-@p < 1000 then 'true' else variable_value-@p end
 true
@@ -27,10 +30,15 @@ id	value
 1	10001
 2	2
 BEGIN;
+connection con2;
+connection con1;
 SELECT COUNT(*) FROM t1;
 COUNT(*)
 9998
 COMMIT;
+connection default;
+disconnect con1;
+disconnect con2;
 OPTIMIZE TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	optimize	status	OK

storage/rocksdb/mysql-test/rocksdb/t/disabled.def

@@ -80,7 +80,7 @@ blind_delete_without_tx_api: MDEV-12286: rocksdb.blind_delete_without_tx_api tes
 ##
 information_schema : MariaRocks: requires GTIDs
 mysqlbinlog_gtid_skip_empty_trans_rocksdb : MariaRocks: requires GTIDs
-read_only_tx : MariaRocks: requires GTIDs
+#read_only_tx : MariaRocks: requires GTIDs
 rpl_row_triggers : MariaRocks: requires GTIDs
 
 

storage/rocksdb/mysql-test/rocksdb/t/read_only_tx-master.opt

---rocksdb_default_cf_options=write_buffer_size=16k --log-bin --binlog_format=row --gtid_mode=ON --enforce_gtid_consistency --log-slave-updates
+--rocksdb_default_cf_options=write_buffer_size=16k --log-bin --binlog_format=row --log-slave-updates

storage/rocksdb/mysql-test/rocksdb/t/read_only_tx.test

@@ -2,9 +2,9 @@
 --source include/have_rocksdb.inc
 --source include/count_sessions.inc
 --disable_warnings
---source include/have_gtid.inc
+#--source include/have_gtid.inc
 --enable_warnings
--- let $uuid = `select @@server_uuid;`
+#-- let $uuid = `select @@server_uuid;`
 
 --disable_warnings
 DROP TABLE IF EXISTS t1;
@@ -20,8 +20,8 @@ INSERT INTO t1 VALUES (1,1);
 # Read-only, long-running transaction. SingleDelete/Put shouldn't increase much.
 select variable_value into @p from information_schema.global_status where variable_name='rocksdb_number_sst_entry_put';
 select variable_value into @s from information_schema.global_status where variable_name='rocksdb_number_sst_entry_singledelete';
--- replace_result $uuid uuid
-START TRANSACTION WITH CONSISTENT ROCKSDB SNAPSHOT;
+#-- replace_result $uuid uuid
+START TRANSACTION WITH CONSISTENT SNAPSHOT;
 
 connection con2;
 --disable_query_log