Automatically create the spack environment needed for the spack build system #2028
Description
As far as I understand, at the moment the Spack build system requires passing in a non-None environment (and if you don't you get an unclear error message: #2027), but you also have to create it beforehand (BTW, as far as I can tell the environment is searched in stagedir, not sourcesdir as claimed in the documentation), otherwise the build will fail because the environment doesn't exist.
What about automatically creating an environment in the staging directory if the environment is None, thus making the field optional? If they already have an environment directory that they absolutely want to use that can still do so, but most simple cases users don't need to care about it