Packages can tune the list of files to be archived at the end of install (#7760)

Fixes #2781

This PR introduces a new attribute for packages called
`archive_files`, which designates files that should be saved from
a package build (e.g. the config.log generated during autotools
builds).

The attribute contains a list of glob expressions; Any file that
matches will be archived in the `<prefix>/.spack/archived-files`
directory. Errors that occur when archiving files are collected and
reported in a file named `<prefix>/.spack/archived-files/errors.txt`.

`AutotoolsPackage` and `CMakePackage` provide a sensible default
override for this attribute.

var/spack/repos/builtin.mock/packages/archive-files/package.py

@@ -0,0 +1,53 @@
+##############################################################################
+# Copyright (c) 2013-2018, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Created by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://github.com/spack/spack
+# Please also see the NOTICE and LICENSE files for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License (as
+# published by the Free Software Foundation) version 2.1, February 1999.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
+# conditions of the GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+from spack import *
+
+
+class ArchiveFiles(AutotoolsPackage):
+    """Simple package with one optional dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/a-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+    version('2.0', '2.0_a_hash')
+
+    @property
+    def archive_files(self):
+        return super(ArchiveFiles, self).archive_files + ['../../outside.log']
+
+    def autoreconf(self, spec, prefix):
+        pass
+
+    def configure(self, spec, prefix):
+        pass
+
+    def build(self, spec, prefix):
+        mkdirp(self.build_directory)
+        config_log = join_path(self.build_directory, 'config.log')
+        touch(config_log)
+
+    def install(self, spec, prefix):
+        touch(join_path(prefix, 'deleteme'))