infra-go: add `go vet` to run_tests.sh

Also fix all of the warnings that `go vet` currently reports about this
repo's code.

This run_tests.sh is gradually turning into a fully-loaded presubmit.
We'll probably change its name and run it in a presubmit soon.

BUG=None
TEST=run_tests.sh

Change-Id: Ia92cc9a91c9192fc324bd3664831c7940ceb6770
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/go/+/1688395
Reviewed-by: David Burger <dburger@chromium.org>
Commit-Queue: Sean Abraham <seanabraham@chromium.org>
Tested-by: Sean Abraham <seanabraham@chromium.org>
8 files changed