Configure nova-network database access on debian/ubuntu

The database configuration disappeared from the debian/ubuntu
installation guide. Add the configuration bits in nova.conf, as done for
other distributions.

Change-Id: I7f7c754c7ff8d6898149507b49efd5a9d51e7ef0
Closes-Bug: #1244216
Backport: havana

doc/install-guide/section_nova-network.xml

@@ -68,6 +68,14 @@ flat_network_bridge=br100
 flat_interface=eth1
 public_interface=eth1
 rabbit_host=<replaceable>controller</replaceable></programlisting>
+    </step>
+    <step os="ubuntu;debian">
+      <para>In the multi-host scenario, you also need to configure the database
+      access. Edit <filename>/etc/nova/nova.conf</filename> and set the
+      <code>connection</code> variable in the <literal>[database]</literal>
+      section.</para>
+      <programlisting language="ini">[database]
+connection = mysql://nova:<replaceable>NOVA_DBPASS</replaceable>@<replaceable>controller</replaceable>/nova</programlisting>
     </step>
     <step os="fedora;rhel;centos">
       <para>Provide a local metadata service that is reachable from