install_tree, copy_tree can install into existing directory structures (#8289)

Replace use of `shutil.copytree` with `copy_tree` and `install_tree` functions in `llnl.util.filesystem`.

- `copy_tree` copies without setting permissions.  It should be used to copy files around in the build directory.
- `install_tree` copies files and sets permissions.  It should be used to copy files into the installation directory.
- `install` and `copy` are analogous single-file functions.
- add more extensive tests for these functions
- update packages to use these functions.

var/spack/repos/builtin/packages/kaldi/package.py

@@ -23,7 +23,6 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
 from spack import *
-from distutils.dir_util import copy_tree
 from os.path import join
 from fnmatch import fnmatch
 import os
@@ -105,7 +104,7 @@ def install(self, spec, prefix):
                         install(join(root, name), prefix.bin)
 
             mkdir(prefix.lib)
-            copy_tree('lib', prefix.lib)
+            install_tree('lib', prefix.lib)
 
             for root, dirs, files in os.walk('.'):
                 for name in files: