MB-100: add micro scale xdcr lag test

Change-Id: I09d3f1deb1b18cbd613c17a5ae4a4e2765747138
Reviewed-on: http://review.couchbase.org/24441
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>