permissions: add permission configuration to packages.yaml (#8773)

Spack can now be configured to assign permissions to the files installed by a package.

In the `packages.yaml` file under `permissions`, the attributes `read`, `write`, and `group` control the package permissions. These attributes can be set per-package, or for all packages under `all`. If permissions are set under `all` and for a specific package, the package-specific settings take precedence.  The `read` and `write` attributes take one of `user`, `group`, and `world`.

   packages:
    all:
      permissions:
        write: group
        group: spack
    my_app:
      permissions:
        read: group
        group: my_team

lib/spack/llnl/util/filesystem.py

@@ -242,6 +242,25 @@ def group_ids(uid=None):
     return [g.gr_gid for g in grp.getgrall() if user in g.gr_mem]
 
 
+def chgrp(path, group):
+    """Implement the bash chgrp function on a single path"""
+    gid = grp.getgrnam(group).gr_gid
+    os.chown(path, -1, gid)
+
+
+def chmod_x(entry, perms):
+    """Implements chmod, treating all executable bits as set using the chmod
+    utility's `+X` option.
+    """
+    mode = os.stat(entry).st_mode
+    if os.path.isfile(entry):
+        if not mode & (stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH):
+            perms &= ~stat.S_IXUSR
+            perms &= ~stat.S_IXGRP
+            perms &= ~stat.S_IXOTH
+    os.chmod(entry, perms)
+
+
 def copy_mode(src, dest):
     """Set the mode of dest to that of src unless it is a link.
     """
@@ -413,12 +432,14 @@ def get_filetype(path_name):
     return output.strip()
 
 
-def mkdirp(*paths):
+def mkdirp(*paths, **kwargs):
     """Creates a directory, as well as parent directories if needed."""
+    mode = kwargs.get('mode', stat.S_IRWXU | stat.S_IRWXG | stat.S_IRWXO)
     for path in paths:
         if not os.path.exists(path):
             try:
-                os.makedirs(path)
+                os.makedirs(path, mode)
+                os.chmod(path, mode)  # For systems that ignore makedirs mode
             except OSError as e:
                 if e.errno != errno.EEXIST or not os.path.isdir(path):
                     raise e