Move archive_version setting to if block
Move archive_version setting to if block

The archive_version variable should only get set if versions will be
checked and that is only if there is a list_url in the package file. For
VCS repos setting the variable triggers an error from web.py as it
parses the default_fetcher object.

This should fix #1422.

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