tests: python: fix test820RHBZ912499.py

This tests adding a running libvirt domain to libguestfs.
This was never really a safe real-world example AFAICT because it
creates qemu overlays on top of disks that are opened writeable
by the source guest.

Nowadays qemu uses write locks to reject this type of behavior,
and the test fails.

Adjust things so the source VM opens its storage readonly, but
we are still confirming that add_libvirt_dom doesn't mess up
selinux labels.

Signed-off-by: Cole Robinson <crobinso@redhat.com>

python/t/test820RHBZ912499.py

@@ -45,6 +45,9 @@ class Test820RHBZ912499(unittest.TestCase):
                                for _ in range(8))
         self.domname = "tmp-" + self.domname
 
+        # Pick any old static label
+        self.label = "system_u:system_r:svirt_t:s0:c392,c662"
+
         self.xml = """
 <domain type='qemu'>
   <name>%s</name>
@@ -57,12 +60,17 @@ class Test820RHBZ912499(unittest.TestCase):
   <devices>
     <disk type='file' device='disk'>
       <driver name='qemu' type='raw'/>
-      <source file='%s'/>
-      <target dev='hda' bus='ide'/>
+      <source file='%s'>
+        <seclabel model='selinux' relabel='yes'>
+          <label>%s</label>
+        </seclabel>
+      </source>
+      <readonly/>
+      <target dev='vda' bus='virtio'/>
     </disk>
   </devices>
 </domain>
-""" % (self.domname, self.filename)
+""" % (self.domname, self.filename, self.label)
 
     def test_rhbz912499(self):
         import libvirt
@@ -78,6 +86,7 @@ class Test820RHBZ912499(unittest.TestCase):
         print("before starting libguestfs")
         before = check_output(["ls", "-Z", self.filename])
         print("disk label = %s" % before)
+        self.assertTrue(self.label, str(before).split()[0])
 
         # Now see if we can open the domain with libguestfs without
         # disturbing the label.