qemu: Allow the user to specify vendor and product for disk

QEMU supports setting vendor and product strings for disk since
1.2.0 (only scsi-disk, scsi-hd, scsi-cd support it), this patch
exposes it with new XML elements <vendor> and <product> of disk
device.

docs/formatdomain.html.in

@@ -1657,6 +1657,18 @@
         of 16 hexadecimal digits.
         <span class='since'>Since 0.10.1</span>
       </dd>
+      <dt><code>vendor</code></dt>
+      <dd>If present, this element specifies the vendor of a virtual hard
+        disk or CD-ROM device. It must not be longer than 8 printable
+        characters.
+        <span class='since'>Since 1.0.1</span>
+      </dd>
+      <dt><code>product</code></dt>
+      <dd>If present, this element specifies the product of a virtual hard
+        disk or CD-ROM device. It must not be longer than 16 printable
+        characters.
+        <span class='since'>Since 1.0.1</span>
+      </dd>
       <dt><code>host</code></dt>
       <dd>The <code>host</code> element supports 4 attributes, viz.  "name",
         "port", "transport" and "socket", which specify the hostname, the port

docs/schemas/domaincommon.rng

@@ -905,6 +905,20 @@
           <ref name="wwn"/>
         </element>
       </optional>
+      <optional>
+        <element name="vendor">
+          <data type="string">
+            <param name="pattern">[x20-x7E]{0,8}</param>
+          </data>
+        </element>
+      </optional>
+      <optional>
+        <element name="product">
+          <data type="string">
+            <param name="pattern">[x20-x7E]{0,16}</param>
+          </data>
+        </element>
+      </optional>
     </interleave>
   </define>
   <define name="snapshot">