Replace calling of upstream git_clone for ovs &dpdk

[Michal Ptacek]

In order to provide required versatility and time-to-time we are upgrading ovs / dpdk versions based on commit id, which is not supported in upstream devstack. We need to implement this locally as our original attempt to get this support to upstream failed
https://review.openstack.org/#/c/235818/

current implementation from https://review.openstack.org/#/c/235334
recently stopped working (most likely after I39376914f8bfc286a308c99db6bc92cddab195b5 devstack change)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/418443

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/418443
Committed: https://git.openstack.org/cgit/openstack/networking-ovs-dpdk/commit/?id=1dc86d929f74b0f16b0856d366b34bc3527c6bda
Submitter: Jenkins
Branch: master

commit 1dc86d929f74b0f16b0856d366b34bc3527c6bda
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Tue Jan 10 15:18:00 2017 +0000

    Replace calling of devstack 'git_clone' function.

    The function implemented in this repository allows
    the use of commit ids for 'git clone' and 'git checkout'
    actions.

    Change-Id: I4cbaa1e762c6ce2f4dc9f7b85a1bae9db21335e6
    Closes-Bug: #1651135