Fix bug in `spack debug create-db-tarball`
Fix bug in `spack debug create-db-tarball`

- Fix a bug handling '/' characters in branch names.

- Make tarballs use a descriptive name for the top-level directory, not
  just `opt`.

tmerrick1/spack,tmerrick1/spack,skosukhin/spack,lgarren/spack,TheTimmy/spack,LLNL/spack,EmreAtes/spack,lgarren/spack,TheTimmy/spack,LLNL/spack,matthiasdiener/spack,krafczyk/spack,skosukhin/spack,TheTimmy/spack,lgarren/spack,LLNL/spack,TheTimmy/spack,krafczyk/spack,lgarren/spack,lgarren/spack,LLNL/spack,tmerrick1/spack,mfherbst/spack,matthiasdiener/spack,EmreAtes/spack,LLNL/spack,EmreAtes/spack,krafczyk/spack,skosukhin/spack,mfherbst/spack,matthiasdiener/spack,krafczyk/spack,tmerrick1/spack,iulian787/spack,iulian787/spack,mfherbst/spack,EmreAtes/spack,tmerrick1/spack,matthiasdiener/spack,skosukhin/spack,mfherbst/spack,matthiasdiener/spack,iulian787/spack,EmreAtes/spack,TheTimmy/spack,iulian787/spack,iulian787/spack,skosukhin/spack,krafczyk/spack,mfherbst/spack