spack: Add package (#25979)

* Make python 2 use 'from __future__ import absolute_import' to allow import spack.pkgkit

* Add Spack

* Improve ranges

lib/spack/spack/repo.py

@@ -78,7 +78,7 @@ def get_full_namespace(namespace):
 #:
 #: TODO: At some point in the future, consider removing ``from spack import *``
 #: TODO: from packages and shifting to from ``spack.pkgkit import *``
-_package_prepend = 'from spack.pkgkit import *'
+_package_prepend = 'from __future__ import absolute_import; from spack.pkgkit import *'
 
 
 def autospec(function):