Automatic merge from submit-queue (batch tested with PRs 42128, 42064, 42253, 42309, 42322)

Default E2E_ZONES to empty string.

Also print an error message and exit if host cluster context cannot be derived.

I don't think we should do any of this magic. This is a stop gap solution to get all our tests to stable state. I will actively get rid of all this defaulting magic once our main tests are stable.

cc @kubernetes/sig-federation-pr-reviews