MB-8045: bumped default number of moves before compaction to 64

I.e. our perf data suggests that 64 doesn't blow up disk space usage
too much and saves a ton of time on rebalance.

Change-Id: Iac1f8a2caa3e97f6eaf1b2d427fb257f43e31e09
Reviewed-on: http://review.couchbase.org/25571
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>