relicense: replace LGPL headers with Apache-2.0/MIT SPDX headers

- remove the old LGPL license headers from all files in Spack
- add SPDX headers to all files
  - core and most packages are (Apache-2.0 OR MIT)
  - a very small number of remaining packages are LGPL-2.1-only

share/spack/qa/run-doc-tests

@@ -1,4 +1,10 @@
 #!/bin/bash -e
+#
+# Copyright 2013-2018 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
 #
 # Description:
 #     Builds Spack documentation and checks for