MB-100: print memory usage when ram quota < 100MB

Change-Id: Ib4f9d69b0856eac06e9c8473a46e3ab3bdf854f0
Reviewed-on: http://review.couchbase.org/24771
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>