Relax python dependencys refs: Juniper/contrail-packages#79

(cherry-picked from commit 4a73c172444a460da6624ec300f3d3e3484abc5b)

Backported from https://github.com/Juniper/contrail-controller/pull/712
Refs http://lists.opencontrail.org/pipermail/dev_lists.opencontrail.org/2014-May/001047.html