Simplify the tests that are present in MySQL 5.7. Make the table
smaller while generating enough undo log. Do not unnecessarily
drop tables.

trx_purge_initiate_truncate(): Remove two crash injection points
(before and after normal redo log checkpoint), because they are
not adding any value. Clarify some messages.

trx_sys_create_rsegs(): Display the number of active undo tablespaces.

srv_undo_tablespaces_init(): When initializing the data files, do not
leave srv_undo_tablespaces_active at 0.
Do not display that number; let trx_sys_create_rsegs() display it once
the final number is known.

innodb_params_adjust(): Adjust parameters after startup.

innobase_init(): Do not allow innodb_max_undo_size to be less
than SRV_UNDO_TABLESPACE_SIZE_IN_PAGES. This avoids unnecessary
repeated truncation of undo tablespaces when using
innodb_page_size=32k or innodb_page_size=64k.