Disable mlockall by default.

Because we switched to R16 and it's known to cause problems.

Change-Id: I7546e2122ab7427d494a8556aa54f604efb8c152
Reviewed-on: http://review.couchbase.org/36285
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>