[arch-guide] Make menu under design consistent and not redundant

- Changed all of the section titles under design for consistency
- Removed design from menu items under design because it was redundant

Change-Id: Ia696a19c1cd579c3e0ee72cc52feb427762a4165

doc/arch-design/source/design-cmp-tools.rst

@@ -1,6 +1,6 @@
-===============================
-Cloud management platform tools
-===============================
+=============================
+Cloud management architecture
+=============================
 
 Complex clouds, in particular hybrid clouds, may require tools to
 facilitate working across multiple clouds.

doc/arch-design/source/design-compute.rst

@@ -1,6 +1,6 @@
-===================
-Compute node design
-===================
+====================
+Compute architecture
+====================
 
 .. toctree::
   :maxdepth: 3

doc/arch-design/source/design-control-plane.rst

@@ -1,6 +1,6 @@
-=============
-Control Plane
-=============
+==========================
+Control plane architecture
+==========================
 
 .. From Ops Guide chapter: Designing for Cloud Controllers and Cloud
    Management

doc/arch-design/source/design-identity.rst

@@ -1,3 +1,3 @@
-========
-Identity
-========
+=====================
+Identity architecture
+=====================

doc/arch-design/source/design-images.rst

@@ -1,3 +1,3 @@
-======
-Images
-======
+==========================
+Image Service architecture
+==========================

doc/arch-design/source/design-networking.rst

@@ -1,8 +1,8 @@
 .. _network-design:
 
-==========
-Networking
-==========
+====================
+Network architecture
+====================
 
 .. toctree::
    :maxdepth: 2

doc/arch-design/source/design-storage.rst

@@ -1,6 +1,6 @@
-==============
-Storage design
-==============
+====================
+Storage architecture
+====================
 
 Storage is found in many parts of the OpenStack cloud environment. This
 chapter describes storage type, design considerations and options when