oeqa/utils: {Target,SDK,}BuildProject remove dependency of bb

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.

[YOCTO #10231]
[YOCTO #10599]

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>