metadata: group metadata next to description

It's better to group all the metadata together.  This is a
cosmetic output change; since the RNG allows interleave, it
doesn't matter where the user stuck it on input, and an XPath
query will find the same information when parsing the output.

* src/conf/domain_conf.c (virDomainDefFormatInternal): Output
metadata earlier.
* docs/formatdomain.html.in: Update documentation.
* tests/domainsnapshotxml2xmlout/metadata.xml: Update test.
* tests/qemuxml2xmloutdata/qemuxml2xmlout-metadata.xml: Likewise.

tests/qemuxml2xmloutdata/qemuxml2xmlout-metadata.xml

@@ -1,6 +1,10 @@
 <domain type='qemu'>
   <name>QEMUGuest1</name>
   <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <metadata>
+    <app1:foo xmlns:app1="http://foo.org/">fooish</app1:foo>
+    <app2:bar xmlns:app2="http://bar.com/" maman="baz">barish</app2:bar>
+  </metadata>
   <memory>219100</memory>
   <currentMemory>219100</currentMemory>
   <vcpu cpuset='1-4,8-20,525'>1</vcpu>
@@ -22,8 +26,4 @@
     <controller type='ide' index='0'/>
     <memballoon model='virtio'/>
   </devices>
-  <metadata>
-    <app1:foo xmlns:app1="http://foo.org/">fooish</app1:foo>
-    <app2:bar xmlns:app2="http://bar.com/" maman="baz">barish</app2:bar>
-  </metadata>
 </domain>