This is to generally warn Google devs about lack of LOAS creds.
Given the switch to RBE, lack of LOAS creds will start resulting in build
failures, so adding a warning message ahead of time to all builds. Will
convert this to a build failure after a week.
We need LOAS creds to be able to even fetch the CDPush config file to
determine whether to use RBE in a build a not, which is why I'm making
this a broad error message across builds.
Test: ran "m nothing" build with / without gcert and with / without
"stubby" in $PATH and confirmed appropriate error message.
Bug: b/235985591
Change-Id: I15cbaf372b0a7b79f868a06c7d5ede19b49ae687
7bc781949a