Fixes the example architecture diagram in operation guide.

Change-Id: If1688d50a14fd877482b41d190f1c806d1e35852
Closes-Bug: #1251543

doc/openstack-ops/ch_arch_example.xml

@@ -311,7 +311,7 @@
             <mediaobject>
                 <imageobject>
                     <imagedata width="4in"
-                        fileref="figures/os_physical_network_1.png"/>
+                        fileref="figures/os_physical_network.png"/>
                 </imageobject>
             </mediaobject>
         </informalfigure>