snapshot: Rename qemu domain snapshot test files

Make it obvious that the domainsnapshotxml2xml test is only run when
compiling in support for qemu.

Suggested-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Acked-by: Peter Krempa <pkrempa@redhat.com>

tests/qemudomainsnapshotxml2xmlout/disk-seclabel.xml

@@ -0,0 +1,15 @@
+<domainsnapshot>
+  <name>my snap name</name>
+  <description>!@#$%^</description>
+  <creationTime>581484660</creationTime>
+  <disks>
+    <disk name='hde' snapshot='external' type='file'>
+      <source file='/path/to/new2'>
+        <seclabel model='dac' relabel='no'/>
+      </source>
+    </disk>
+  </disks>
+  <domain>
+    <uuid>9d37b878-a7cc-9f9a-b78f-49b3abad25a8</uuid>
+  </domain>
+</domainsnapshot>