Change eth0 to eth2 in Ops Guide Networking Diagram

1) Built a new version of figure 12.2 replacing eth0 with eth2
and clearing up shape overlaps from the original diagram.
2) Changed references to the internet facing eth0 to eth2
in the text corresponding to figure 12.2.

Change-Id: Iedbcb1de123627158a67dd97e820158d844be9f2
backport:none
Closes-Bug: #1372516

doc/openstack-ops/ch_ops_network_troubleshooting.xml

@@ -556,14 +556,14 @@ output:52,output:51,output:50,output:55,output:33
       <listitem>
         <para>The <code>qg-&lt;n&gt;</code> interface in the l3-agent router
         namespace sends the packet on to its next hop through device
-        <code>eth0</code> on the external bridge <code>br-ex</code>. This
+        <code>eth2</code> on the external bridge <code>br-ex</code>. This
         bridge is constructed similarly to <code>br-eth1</code> and may be
         inspected in the same way.</para>
       </listitem>
 
       <listitem>
         <para>This external bridge also includes a physical network interface,
-        <code>eth0</code> in this example, which finally lands the packet on
+        <code>eth2</code> in this example, which finally lands the packet on
         the external network destined for an external router or
         destination.</para>
       </listitem>