LU-10680 mdd: disable changelog garbage collection by default

LU-10680 mdd: disable changelog garbage collection by default

Changelog garbage collection has introduced some instability so
disable it by default.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I708198d76af060cb796de89266ee74a968f92ac1
Reviewed-on: https://review.whamcloud.com/31552
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>