adding a fallback on failure with git --depth
adding a fallback on failure with git --depth

Certain remote protocols don't support the `--depth` option.  Since this can't
be checked by URL type or in any sane way locally, this version attempts to
clone git repositories with the --depth option, and if that fails attempts the
clone again without it.

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