got wrong arch when building installer

[pkking]

I have a repo that has both i686 and x86_64 anaconda like buildlogs.centos.org, when i build a installer on a amd64 machine, lorax init its buildarch with i686 because it just use first anaconda's arch(which is anaconda.i686) in yum repo.
Solved by passing a --buildarch to lorax in install.py, i dont know if it is a issue for us but still post it here and maybe @jperrin 's issue has something related to this :)