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/rockstar/package.py

@@ -22,10 +22,8 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-
 import os
 from spack import *
-from distutils.dir_util import copy_tree
 
 
 class Rockstar(MakefilePackage):
@@ -59,7 +57,7 @@ def build(self, spec, prefix):
 
     def install(self, spec, prefix):
         # Install all files and directories
-        copy_tree(".", prefix)
+        install_tree('.', prefix)
 
         mkdir(prefix.bin)
         mkdir(prefix.lib)