misc: support unset variables in lhci dogfood script (#9745)
misc: support unset variables in lhci dogfood script (#9745)


wardpeet/lighthouse,GoogleChrome/lighthouse,umaar/lighthouse,GoogleChrome/lighthouse,umaar/lighthouse,GoogleChrome/lighthouse,GoogleChrome/lighthouse,wardpeet/lighthouse,wardpeet/lighthouse,GoogleChrome/lighthouse,wardpeet/lighthouse,ev1stensberg/lighthouse,ev1stensberg/lighthouse,ev1stensberg/lighthouse,ev1stensberg/lighthouse,wardpeet/lighthouse,umaar/lighthouse,umaar/lighthouse