Change tox targets to use new build.py
Change tox targets to use new build.py

tox -e images-centos-binary
tox -e images-centos-source

Both above now execute parallel image building script.

Change-Id: I6a4174b184fc239c6baa950a9c787fc6ad220774
Paritally-Implements: blueprint gate-source-builds

negronjl/kolla,fdumpling/kolla,nihilifer/kolla,negronjl/kolla,stackforge/kolla,chenzhiwei/kolla,tonyli71/kolla,LoHChina/kolla,toby82/kolla,mandre/kolla,stackforge/kolla,jakedahn/kolla,chenzhiwei/kolla,mrangana/kolla,jakedahn/kolla,rahulunair/kolla,rahulunair/kolla,coolsvap/kolla,openstack/kolla,limamauricio/mykolla,GalenMa/kolla,stackforge/kolla,limamauricio/mykolla,nihilifer/kolla,chenzhiwei/kolla,GalenMa/kolla,fdumpling/kolla,HackToday/kolla,jakedahn/kolla,dardelean/kolla-ansible,LoHChina/kolla,rajalokan/kolla,coolsvap/kolla,HackToday/kolla,intel-onp/kolla,rajalokan/kolla,LoHChina/kolla,intel-onp/kolla,toby82/kolla,mandre/kolla,negronjl/kolla,mandre/kolla,fdumpling/kolla,coolsvap/kolla,openstack/kolla,rajalokan/kolla,toby82/kolla,HackToday/kolla,dardelean/kolla-ansible,tonyli71/kolla,dardelean/kolla-ansible,limamauricio/mykolla,mrangana/kolla