Network: Add support for DNS hosts definition to the network XML

This commit introduces names definition for the DNS hosts file using
the following syntax:

  <dns>
    <host ip="192.168.1.1">
      <name>alias1</name>
      <name>alias2</name>
    </host>
  </dns>

Some of the improvements and fixes were done by Laine Stump so
I'm putting him into the SOB clause again ;-)

Signed-off-by: Michal Novotny <minovotn@redhat.com>
Signed-off-by: Laine Stump <laine@laine.org>

docs/formatnetwork.html.in

@@ -184,6 +184,14 @@
             or commas. value is a single string that can contain multiple values
             separated by commas. <span class="since">Since 0.9.3</span>
           </dd>
+          <dt><code>host</code></dt>
+          <dd>The <code>host</code> element within <code>dns</code> is the
+            definition of DNS hosts to be passed to the DNS service. The IP
+            address is identified by the <code>ip</code> attribute and the names
+            for that IP address are identified in the <code>hostname</code>
+            sub-elements of the <code>host</code> element.
+            <span class="since">Since 0.9.3</span>
+          </dd>
         </dl>
       </dd>
       <dt><code>dhcp</code></dt>

docs/schemas/network.rng

@@ -97,6 +97,14 @@
                   <attribute name="value"><text/></attribute>
                 </element>
               </zeroOrMore>
+              <zeroOrMore>
+                <element name="host">
+                  <attribute name="ip"><ref name="ipv4-addr"/></attribute>
+                  <oneOrMore>
+                    <element name="hostname"><text/></element>
+                  </oneOrMore>
+                </element>
+              </zeroOrMore>
             </element>
         </optional>