gitignore everything in /etc/spack except /etc/spack/defaults (#4459)
gitignore everything in /etc/spack except /etc/spack/defaults (#4459)

* gitignore everything in /etc/spack except /etc/spack/defaults

* Don't ignore subsubdirectories of /etc/spack/defaults

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