Add support for "Storing InnoDB Undo Logs in Separate Tablespaces"

[ShahriyarR]

Update PTB to use -> https://dev.mysql.com/doc/refman/5.7/en/innodb-undo-tablespace.html

This feature involves the following new or renamed configuration options:

innodb_undo_tablespaces

innodb_undo_directory

innodb_rollback_segments becomes innodb_undo_logs. The old name is still available for compatibility. 

[ShahriyarR]

So the decided values is:

innodb_undo_tablespaces=10
innodb_undo_directory -> will not specify. By default path is datadir.
innodb_undo_logs=128(max value)

[ShahriyarR]

Implemented. Fixed.

[RoelVdP]

One question; with innodb_undo_logs=128 (max value) - is the performance about the same? If the queries per second (qps) is much lower, then the testing coverage is more limited, for example.