oeqa/utils: {Target,SDK,}BuildProject remove dependency of bb
Don't use bitbake references inside utils modules, in order todo
that changes getVar calls for arguments in the __init__ method like
dl_dir for all the classes and testlogdir, builddatetime in
SDKBUildProject.
Also don't export proxies inside _download_archive method, a good
practice is to setup the proxies at init of the process instead of
do it in this helper module.
