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/docker/build/common/handle-prompt.sh

@@ -1,3 +1,8 @@
+# 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)
+
 __tmp="`mktemp -d`"
 
 __trylock() {

share/spack/docker/build/common/handle-ssh.sh

@@ -1,3 +1,8 @@
+# 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)
+
 uid="`id -u`"
 if [ "$uid" '=' '0' ] ; then
     for key_type in dsa ecdsa ed25519 rsa ; do