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/gurobi/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
 import os
 
 
@@ -58,5 +57,4 @@ def setup_environment(self, spack_env, run_env):
         run_env.set('GUROBI_HOME', self.prefix)
 
     def install(self, spec, prefix):
-        with working_dir('linux64'):
-            copy_tree('.', prefix)
+        install_tree('linux64', prefix)