Add systemtap script for tracking down large allocations.

Change-Id: I057f67bbd8b1e431c6b95fd15c20faa5ff98bb94
Reviewed-on: http://review.couchbase.org/38999
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>