Reason:
======
undo_space_dblwr test case fails if the first page of undo
tablespace is not flushed before restart the server. While
restarting the server, InnoDB fails to detect the first
page of undo tablespace from doublewrite buffer.

Fix:
===
Use "ib_log_checkpoint_avoid_hard" debug sync point
to avoid checkpoint and make sure to flush the
dirtied page before killing the server.

innodb_make_page_dirty(): Fails to set
srv_fil_make_page_dirty_debug variable.