Update basic environment content for Juno

I updated the basic environment content in the installation
guide for Juno as follows:

1) Collapsed database section because it only includes procedures
   for the controller. Although the diagrams show the database on
   the controller node, I added some text to remind users.
2) Reorganized sections to improve flow. For example, moving the
   security section closer to the beginning of the chapter.

Change-Id: Icd43c2530982d356067c8a77ba4a744a2c63e0e4

doc/install-guide/ch_basic_environment.xml

@@ -45,10 +45,10 @@
     </para>
   </note>
   <xi:include href="section_basics-prerequisites.xml"/>
+  <xi:include href="section_basics-security.xml"/>
   <xi:include href="section_basics-networking.xml"/>
   <xi:include href="section_basics-ntp.xml"/>
-  <xi:include href="section_basics-security.xml"/>
-  <xi:include href="section_basics-database.xml"/>
   <xi:include href="section_basics-packages.xml"/>
+  <xi:include href="section_basics-database.xml"/>
   <xi:include href="section_basics-queue.xml"/>
 </chapter>

doc/install-guide/section_basics-database.xml

@@ -7,12 +7,11 @@
   <?dbhtml stop-chunking?>
   <title>Database</title>
   <para>Most OpenStack services use an SQL database to store information.
-    The procedures in this guide use <application>MariaDB</application>
+    The database typically runs on the controller node. The procedures in
-    or <application>MySQL</application> depending on the distribution.
+    this guide use <application>MariaDB</application> or
+    <application>MySQL</application> depending on the distribution.
     OpenStack services also support other SQL databases including
     <link xlink:href="http://www.postgresql.org/">PostgreSQL</link>.</para>
-  <section xml:id="basics-database-controller-node">
-    <title>Controller node</title>
   <procedure>
     <title>To install and configure the database server</title>
     <step>
@@ -89,5 +88,4 @@ character-set-server = utf8</programlisting>
       <screen><prompt>#</prompt> <userinput>mysql_secure_installation</userinput></screen>
     </step>
   </procedure>
-  </section>
 </section>