Add third-party library for python-rrdtool, used by kwapi.

Change-Id: I9cad78d423878a4b78f52e68effcbc26c387fa80
Reviewed-on: https://review.openstack.org/35697
Reviewed-by: François Rossigneux <francois.rossigneux@inria.fr>
Reviewed-by: Khai Do <zaro0508@gmail.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins