Fix #11240 (#11995)

* extends mkdirs with permissions for intermediate folders

Does not use os.makedirs mode parameter because its behavior is changed
with Python 3.7 (it ignores it for intermediate dirs), and moreover it
was not possible to set different modes for newly-created folders
and leaf folder.

reference:
- https://bugs.python.org/issue19930
- https://docs.python.org/3.7/library/os.html#os.makedirs

* comment mkdirp step easing code understanding

* revert mkdir to default for package metapath

since metapath is nested in package folder, there is no need
to specify permissions for intermediate folders because the prefix
already exists.

* comment create_install_directory package modes

lib/spack/llnl/util/filesystem.py

@@ -423,14 +423,39 @@ def mkdirp(*paths, **kwargs):
     Keyword Aguments:
         mode (permission bits or None, optional): optional permissions to
             set on the created directory -- use OS default if not provided
+        mode_intermediate (permission bits or None, optional):
+            same as mode, but for newly-created intermediate directories
     """
     mode = kwargs.get('mode', None)
+    mode_intermediate = kwargs.get('mode_intermediate', None)
     for path in paths:
         if not os.path.exists(path):
             try:
+                intermediate_folders = []
+                if mode_intermediate is not None:
+                    # detect missing intermediate folders
+                    intermediate_path = os.path.dirname(path)
+
+                    while intermediate_path:
+                        if os.path.exists(intermediate_path):
+                            break
+
+                        intermediate_folders.append(intermediate_path)
+                        intermediate_path = os.path.dirname(intermediate_path)
+
+                # create folders
                 os.makedirs(path)
+
+                # leaf folder permissions
                 if mode is not None:
                     os.chmod(path, mode)
+
+                # for intermediate folders, change mode just for newly created
+                # ones and if mode_intermediate has been specified, otherwise
+                # intermediate folders list is not populated at all and default
+                # OS mode will be used
+                for intermediate_path in reversed(intermediate_folders):
+                    os.chmod(intermediate_path, mode_intermediate)
             except OSError as e:
                 if e.errno != errno.EEXIST or not os.path.isdir(path):
                     raise e