CBD-1349: Added elapsed time feature.

Change-Id: I5f386f2e9a7789fc8fdb8201207b3488a2f06875
Reviewed-on: http://review.couchbase.org/35899
Reviewed-by: Philip Labee <philip@couchbase.com>
Reviewed-by: Eric Limare <eric.limare@couchbase.com>
Tested-by: Eric Limare <eric.limare@couchbase.com>