Expand cabal-tests --help

[andreasabel]

Lifted from #8392 (comment):
Currently:

$ cabal-tests --help
Invalid option `--help'

Usage: cabal-tests [-j INT] [FILE] [--hide-successes] [-v|--verbose] 
                   [-q|--quiet] [--builddir DIR] [--with-cabal PATH] 
                   [-w|--with-ghc PATH] [--with-hackage-repo-tool PATH] 
                   [--with-haddock PATH] [--accept] [--skip-setup-tests]

I would want more information on the meaning of:

• FILE
• --skip-setup-tests
• Any non-standard behavior of --with-PROG options, see:
  • cabal-tests --with-cabal should have sensible default #8401