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/go/package.py

@@ -23,8 +23,6 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
 import os
-import shutil
-import glob
 import llnl.util.tty as tty
 from spack import *
 
@@ -101,15 +99,7 @@ def install(self, spec, prefix):
         with working_dir('src'):
             bash('{0}.bash'.format('all' if self.run_tests else 'make'))
 
-        try:
-            os.makedirs(prefix)
-        except OSError:
-            pass
-        for f in glob.glob('*'):
-            if os.path.isdir(f):
-                shutil.copytree(f, os.path.join(prefix, f))
-            else:
-                shutil.copy2(f, os.path.join(prefix, f))
+        install_tree('.', prefix)
 
     def setup_environment(self, spack_env, run_env):
         spack_env.set('GOROOT_FINAL', self.spec.prefix)
@@ -123,10 +113,9 @@ def setup_dependent_package(self, module, dependent_spec):
 
         In most cases, extensions will only need to set GOPATH and use go::
 
-        env = os.environ
         env['GOPATH'] = self.source_path + ':' + env['GOPATH']
         go('get', '<package>', env=env)
-        shutil.copytree('bin', os.path.join(prefix, '/bin'))
+        install_tree('bin', prefix.bin)
         """
         #  Add a go command/compiler for extensions
         module.go = self.spec['go'].command