LU-10773 obdclass: yield cpu during changelog_block_trim_ext

LU-10773 obdclass: yield cpu during changelog_block_trim_ext

To avoid soft-lockup if there are too many records to be handled.
The patch also filters out zero-sized records to avoid dead loop.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ia094f9153b5ef2602103d2ee13ee7ad3ffe6dc4f
Reviewed-on: https://review.whamcloud.com/31516
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>