customize bootstrap upload path via env var
customize bootstrap upload path via env var

this can also be achieved by each job appending their own flag
--upload="gs://other-bucket/other-path", but env vars are something
we could inject in via a prow preset if we wanted to change all jobs
to upload someplace new en-masse without necessarily touching all jobs

monopole/test-infra,BenTheElder/test-infra,ixdy/kubernetes-test-infra,cblecker/test-infra,jessfraz/test-infra,dims/test-infra,cjwagner/test-infra,BenTheElder/test-infra,cjwagner/test-infra,cjwagner/test-infra,pwittrock/test-infra,BenTheElder/test-infra,fejta/test-infra,michelle192837/test-infra,fejta/test-infra,monopole/test-infra,monopole/test-infra,pwittrock/test-infra,brahmaroutu/test-infra,kubernetes/test-infra,fejta/test-infra,kubernetes/test-infra,dims/test-infra,michelle192837/test-infra,brahmaroutu/test-infra,pwittrock/test-infra,monopole/test-infra,dims/test-infra,dims/test-infra,cjwagner/test-infra,cjwagner/test-infra,dims/test-infra,michelle192837/test-infra,BenTheElder/test-infra,kubernetes/test-infra,monopole/test-infra,jessfraz/test-infra,pwittrock/test-infra,brahmaroutu/test-infra,kubernetes/test-infra,fejta/test-infra,ixdy/kubernetes-test-infra,michelle192837/test-infra,michelle192837/test-infra,brahmaroutu/test-infra,cjwagner/test-infra,jessfraz/test-infra,cblecker/test-infra,cblecker/test-infra,jessfraz/test-infra,BenTheElder/test-infra,jessfraz/test-infra,pwittrock/test-infra,kubernetes/test-infra,fejta/test-infra,ixdy/kubernetes-test-infra,kubernetes/test-infra,cblecker/test-infra,jessfraz/test-infra,cblecker/test-infra,fejta/test-infra,BenTheElder/test-infra,brahmaroutu/test-infra,monopole/test-infra,michelle192837/test-infra,ixdy/kubernetes-test-infra,brahmaroutu/test-infra,ixdy/kubernetes-test-infra,dims/test-infra,cblecker/test-infra