Move completed goals into the completed directory

As per the new structure of community-wide goal[1],
we will keep all the completed goals into separate
directory 'goals/completed/' which will help to
track the goals and a clear view on what all goals
still need more work.

Keeping 'Migrate from oslo.rootwrap to oslo.privsep'
goal in the selected directory only as this still need to
finish the work. Rest all previous cycle goals are moved
to 'goals/completed/' directory

[1] https://governance.openstack.org/tc/goals/#completing-goals

Change-Id: I6c0d979038f65abb091db646ddb4c0d09c43735a

goals/completed/index.rst

@@ -0,0 +1,10 @@
+===============
+Completed goals
+===============
+
+.. toctree::
+   :glob:
+   :maxdepth: 2
+   :reversed:
+
+   */index

goals/index.rst

@@ -254,7 +254,12 @@ release/time, leaving the projects to focus on whatever is most important
 in their scope.
 
 .. toctree::
-   :maxdepth: 3
+   :maxdepth: 2
 
    selected/index
    proposed/index
+
+.. toctree::
+   :maxdepth: 3
+
+   completed/index

goals/proposed/index.rst

@@ -4,5 +4,7 @@ Proposed goals
 
 .. toctree::
    :glob:
+   :maxdepth: 1
+   :reversed:
 
    *

goals/selected/index.rst

@@ -4,8 +4,7 @@ Selected goals
 
 .. toctree::
    :glob:
-   :maxdepth: 2
+   :maxdepth: 1
    :reversed:
 
-   */index
    *