cmd/frontend: add custom import paths for aws and gcp repos
cmd/frontend: add custom import paths for aws and gcp repos

Change-Id: I4f43f8b727d39ec75aec78de304b402c726a59e1
Reviewed-on: https://upspin-review.googlesource.com/8940
Reviewed-by: Bons <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@google.com>
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

upspin/upspin,upspin/upspin