Added swift as a trove prerequisite

If you want to use trove for database backups,
you need swift.

The install guide does not state this requirement,
which needs to go on the following page:

http://docs.openstack.org/trunk/install-guide/install/apt/content/trove-install.html

The need to add swift is documented in the
following trove doc scrub etherpad:

https://etherpad.openstack.org/p/trove-doc-items

I added the swift info.

Change-Id: I49102b6c961464f14484797f06949540fe400920
Closes-Bug: #1346438

doc/install-guide/section_trove-install.xml

@@ -13,6 +13,14 @@
       OpenStack environment with at least the following components
       installed: Compute, Image Service, Identity.</para>
   </formalpara>
+  <itemizedlist>
+    <listitem>
+      <para>If you want to do backup and restore, you also need Object Storage.</para>
+    </listitem>
+    <listitem>
+      <para>If you want to provision datastores on block-storage volumes, you also need Block Storage.</para>
+    </listitem>
+  </itemizedlist>
   <para>To install the Database module on the controller:</para>
   <procedure>
     <step>
@@ -23,11 +31,8 @@
       <screen os="opensuse;sles"><prompt>#</prompt> <userinput>zypper install openstack-trove python-troveclient</userinput></screen>
     </step>
     <step os="debian">
-      <para>Respond to the prompts for <link
-        linkend="debconf-dbconfig-common">database management</link> and
-        <link linkend="debconf-keystone_authtoken"
-        ><literal>[keystone_authtoken]</literal> settings</link>,
-        and <link linkend="debconf-api-endpoints">API endpoint</link>
+      <para>Respond to the prompts for <link xlink:href="debconf-dbconfig-common">database management</link> and <link xlink:href="debconf-keystone_authtoken"><literal>[keystone_authtoken]</literal> settings</link>,
+        and <link xlink:href="debconf-api-endpoints">API endpoint</link>
         registration. The <command>trove-manage db_sync</command>
         command runs automatically.</para>
     </step>