- install and probably other commands were designed to run once, but now
we can to test them from within Spack with SpackCommand
- cmd/install.py assumed that it could modify do_install in PackageBase
and leave it that way; this makes the decorator temporary
- package.py didn't properly initialize its stage if the same package had
been built successfully before (and the stage removed).
- manage stage lifecycle better and remember when Package needs to
re-create the stage
f51b541ef8