Add scripts to help with releases

Cutting releases should be done from clean
checkout sources.

New scripts:
  - utils/lint.sh [branch]
    - checks out clean repo from current dir
    - builds
    - runs tests (runtest, runtest-cluster, runtest-sentinel)
    - aborts on _any_ error
  - utils/tag.sh [branch] [tag]
    - runs lint.sh on branch
    - if all tests pass, tags the branch