Install Guide: Add missing Ubuntu instruction for Neutron install

The step was missing instructions for Ubuntu and Debian, add them.

Change-Id: I065323428c772a718ec45b312104c23db92a14d4
backport: havana
Closes-Bug: #1245750
Closes-Bug: #1241880
(cherry picked from commit 173be34)

doc/install-guide/section_neutron-install.xml

@@ -810,7 +810,8 @@ admin_password=<replaceable>NEUTRON_PASS</replaceable></programlisting>
         <procedure>
           <step>
             <para>Install the Open vSwitch plug-in and its
-              dependencies.</para>
+              dependencies:</para>
+            <screen os="ubuntu;debian"><prompt>#</prompt> <userinput>apt-get install neutron-plugin-openvswitch-agent openvswitch-switch</userinput></screen>
             <screen os="rhel;fedora;centos"><prompt>#</prompt> <userinput>yum install openstack-neutron-openvswitch</userinput></screen>
             <screen os="opensuse;sles"><prompt>#</prompt> <userinput>zypper install openstack-neutron-openvswitch-agent</userinput></screen>
           </step>