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/glib/package.py

@@ -25,7 +25,6 @@
 from spack import *
 
 import os.path
-import shutil
 
 
 class Glib(AutotoolsPackage):
@@ -117,7 +116,7 @@ def fix_dtrace_usr_bin_path(self):
         dtrace_copy = join_path(self.dtrace_copy_path, 'dtrace')
 
         with working_dir(self.dtrace_copy_path, create=True):
-            shutil.copy(dtrace, dtrace_copy)
+            copy(dtrace, dtrace_copy)
             filter_file(
                 '^#!/usr/bin/python',
                 '#!/usr/bin/env python',