fix(instances): a migrated VM's source definition is always removed

Migration left the VM defined on the source host unless "Delete
original" was ticked (VIR_MIGRATE_UNDEFINE_SOURCE). With the shared
storage migration needs, that definition points at the disks the
destination VM is running on: the VM showed on both hosts and could be
started (or autostarted) a second time against the same disks; only a
configured lock manager stops that.

moveto now always passes VIR_MIGRATE_UNDEFINE_SOURCE with
VIR_MIGRATE_PERSIST_DEST. The option is gone from the form, the view,
the API (MigrateSerializer.xml_del) and the clone auto-migration. It
removes the definition, not the disk files.

vrtManager/test_migration.py

@@ -0,0 +1,52 @@
+"""Migration flags: the source definition never stays behind."""
+
+import unittest
+
+import libvirt
+from django.conf import settings
+
+if not settings.configured:
+    settings.configure(MAC_OUI="52:54:10")
+
+from vrtManager.instance import wvmInstances
+
+
+class FakeDomain:
+    def __init__(self):
+        self.calls = []
+
+    def migrate(self, dconn, flags, dname, uri, bandwidth):
+        self.calls.append((flags, uri))
+
+
+class FakeSource:
+    def __init__(self, state):
+        self.state = state
+        self.instance = FakeDomain()
+
+    def get_status(self):
+        return self.state
+
+    def get_arch(self):
+        return "x86_64"
+
+    def get_dom_emulator(self):
+        return "/usr/bin/qemu-system-x86_64"
+
+
+def destination():
+    dest = wvmInstances.__new__(wvmInstances)
+    dest.wvm = object()
+    dest.get_emulator = lambda arch: "/usr/bin/qemu-system-x86_64"
+    return dest
+
+
+class MigrationFlagsTestCase(unittest.TestCase):
+    def test_the_source_definition_is_always_removed(self):
+        for state, live, offline in ((1, True, False), (5, False, True)):
+            with self.subTest(state=state):
+                source = FakeSource(state)
+                destination().moveto(source, "vm", live=live, unsafe=False, offline=offline)
+                flags = source.instance.calls[0][0]
+                self.assertTrue(flags & libvirt.VIR_MIGRATE_UNDEFINE_SOURCE)
+                self.assertTrue(flags & libvirt.VIR_MIGRATE_PERSIST_DEST)