update build command arguments

[vsoch]

It might make sense to provide an extra list of options that the user can provide whatever they please. Here are the most current:

      --builder string    remote Build Service URL, setting this implies
                          --remote (default "https://build.sylabs.io")
  -d, --detached          submit build job and print build ID (no
                          real-time logs and requires --remote)
      --docker-login      login to a Docker Repository interactively
  -f, --fakeroot          build using user namespace to fake root user
                          (requires a privileged installation)
  -F, --force             delete and overwrite an image if it currently exists
  -h, --help              help for build
      --json              interpret build definition as JSON
      --library string    container Library URL (default
                          "https://library.sylabs.io")
      --no-cleanup        do NOT clean up bundle after failed build, can
                          be helpul for debugging
      --nohttps           do NOT use HTTPS, for communicating with local
                          docker registry
  -T, --notest            build without running tests in %test section
  -r, --remote            build image remotely (does not require root)
  -s, --sandbox           build image as sandbox format (chroot directory
                          structure)
      --section strings   only run specific section(s) of deffile (setup,
                          post, files, environment, test, labels, none)
                          (default [all])
      --tmpdir string     specify a temporary directory to use for build
  -u, --update            run definition over existing container (skips header)