This commit ensures that:
- go vet will be run as part of the make verify target
- the vet make-rule script won't be run directly, as generated_files won't be run in that case
- that go vet errors show up in the build log with a start time, finish time, and SUCCESS/FAILED message as part of the verify make rule script
Per Clayton's suggestion, move stuff from cluster/lib/util.sh to
hack/lib/util.sh. Also consolidate ensure-temp-dir and use the
hack/lib/util.sh implementation rather than cluster/common.sh.
This allows us to start building real dependencies into Makefile.
Leave old hack/* scripts in place but advise to use 'make'. There are a few
rules that call things like 'go run' or 'build/*' that I left as-is for now.
