mysqlctl: add MyRocks dir/files to backups

[derekperkins]

Using MyRocks changes the data location from a normal MySQL installation. It leaves an .sdi file in the schema directory, where InnoDB would have an .ibd file. All the actual data however for all schemas is stored in a single .rocksdb directory at the data root, with no table specific files. This PR just adds a new file extension check for .sst to confirm a data directory to backup.

ls $DATADIR/schemaname/
-rw-r----- 1 vitess vitess 7.3K Jan 24 02:18 urls_519.sdi

ls $DATADIR/.rocksdb/
-rw-r----- 1 vitess vitess 8.5K Jan 24 02:18 000003.log
-rw-r----- 1 vitess vitess  18M Jan 24 01:44 000011.sst
-rw-r----- 1 vitess vitess  19M Jan 24 01:44 000012.sst
...
-rw-r----- 1 vitess vitess   16 Jan 23 17:51 CURRENT
-rw-r----- 1 vitess vitess   37 Jan 23 17:51 IDENTITY
-rw-r----- 1 vitess vitess    0 Jan 23 17:51 LOCK
-rw-r----- 1 vitess vitess  42K Jan 24 02:18 LOG
-rw-r----- 1 vitess vitess   13 Jan 23 17:51 MANIFEST-000001
-rw-r----- 1 vitess vitess 3.7K Jan 24 02:18 MANIFEST-000006
-rw-r----- 1 vitess vitess 7.1K Jan 23 17:51 OPTIONS-000008
-rw-r----- 1 vitess vitess 7.1K Jan 23 17:51 OPTIONS-000010

[derekperkins]

There should be no backwards compatibility issues. The only potential side effect is if there were subdirectories that were previously ignored because they contained .sst files and not other db file extensions. Those directories will now be copied and restored. There is nothing that will be excluded that was previously included.

[sougou]

This LGTM. @dkhenry do you have any comments?

[dkhenry]

I would just add that we add a .rocksdb folder to the backup_test to go along with the innodb files there.

[dkhenry]

👍

[derekperkins]

Good call on updating those tests, I don't know how I missed those before.