Problem:
========
 If we increase innodb_undo_logs value during startup. New rollback
segment might get allocated during trx_sys_create_rseg(). Essentially, it
would make these tablesapces active with transaction undo data and purge.
But it doesn't come in active undo tablespaces. so these tablespace would
never get truncated.

Fix:
===
 Increase the number of active undo tablespace when we are assigning the
undo tablespace to the newly assigned rollback segment.
Reviewed-by: Kevin Lewis <kevin.lewis@oracle.com>
Reviewed-by: Debarun Banerjee <debarun.banerjee@oracle.com>
RB: 13746