jiahuif: enable docker-in-docker for cloud-provider-gcp tasks.

JobBuild
23098
08-02 20:13
pull-test-infra-bazel 1423016348308475904 1422986119191990272 1422289218234748928
pull-test-infra-gubernator 1423016348342030336 1422986119238127616 1422289218264109056
pull-test-infra-integration 1423016348488830976 1422986119389122560 1422289218398326784
pull-test-infra-prow-checkconfig 1423016348451082240 1422986119347179520 1422289218364772352
pull-test-infra-verify-file-perms 1423016348375584768 1422986119275876352 1422289218297663488
pull-test-infra-yamllint 1423016348409139200 1422986119313625088 1422289218339606528