lxc-download.in / allow setting keyserver from env
lxc-download.in / allow setting keyserver from env

Checks if DOWNLOAD_KEYSERVER has already been set in the environment before setting a value

Signed-off-by: Tai Kedzierski <11c1a81cf427c048adf7a92a77f0b2bae4d21ce2@gmail.com>

terceiro/lxc,hallyn/lxc,federicobriata/lxc,LynxChaus/lxc,thmo/lxc,aeris/lxc,thmo/lxc,hallyn/lxc,thmo/lxc,aeris/lxc,LynxChaus/lxc,GreatFruitOmsk/lxc,LynxChaus/lxc,caglar10ur/lxc,federicobriata/lxc,GreatFruitOmsk/lxc,caglar10ur/lxc,federicobriata/lxc,GreatFruitOmsk/lxc,hallyn/lxc,terceiro/lxc,ss1h2a3tw/lxc,terceiro/lxc,caglar10ur/lxc,ss1h2a3tw/lxc,ss1h2a3tw/lxc,aeris/lxc