buildcache fixes: index.html & unsigned installs
buildcache fixes: index.html & unsigned installs

This fixes a syntax error in the index.html file generated by the
"spack buildcache" command when creating build caches. This also
fixes support for installing unsigned binaries.
mfherbst/spack,iulian787/spack,tmerrick1/spack,skosukhin/spack,LLNL/spack,TheTimmy/spack,tmerrick1/spack,matthiasdiener/spack,tmerrick1/spack,iulian787/spack,TheTimmy/spack,TheTimmy/spack,tmerrick1/spack,matthiasdiener/spack,mfherbst/spack,lgarren/spack,krafczyk/spack,EmreAtes/spack,skosukhin/spack,LLNL/spack,TheTimmy/spack,TheTimmy/spack,mfherbst/spack,LLNL/spack,mfherbst/spack,lgarren/spack,krafczyk/spack,LLNL/spack,krafczyk/spack,EmreAtes/spack,EmreAtes/spack,skosukhin/spack,krafczyk/spack,lgarren/spack,matthiasdiener/spack,skosukhin/spack,krafczyk/spack,tmerrick1/spack,lgarren/spack,iulian787/spack,EmreAtes/spack,matthiasdiener/spack,skosukhin/spack,EmreAtes/spack,lgarren/spack,iulian787/spack,iulian787/spack,LLNL/spack,mfherbst/spack,matthiasdiener/spack