feat(vrtManager): the libvirt layer's messages show in the reader's language

vrtManager's errors (some 140: a disk that does not move, a network
address outside its subnet, a host device given to another VM, the
disks a migration cannot copy) were English f-strings, so no catalog
could translate them, on pages or in jobs.

They are marked texts with their values now; a variant that differs by
a word (internal or external, running or persistent, with a subnet or
without) is a whole message of its own, and a list of problems is a
list of messages. OperationError reads in the active language, so the
pages that show one translate it as they are; its args stay English, and
so do the logs and the audit log. Host device problems and the Migrate
tab's reasons a disk is not copied are messages too.

vrtManager/tests/test_util.py

@@ -161,6 +161,32 @@ class OperationErrorTestCase(unittest.TestCase):
         # a text without values is not formatted: libvirt's may hold a %
         self.assertEqual(str(OperationError("100% used")), "100% used")
 
+    def test_reads_in_the_active_language_and_keeps_english_in_its_args(self):
+        from django.utils import translation
+        from vrtManager.util import OperationError, message
+
+        error = OperationError("The disks cannot be migrated: %(problems)s", problems=[
+            message("%(target)s: the VM has no disk file to copy", target="vda"),
+            message("%(target)s (%(path)s): %(refusal)s", target="sda", path="/i/os.iso",
+                    refusal=[message("an image is not copied; eject it first")])])
+        english = ("The disks cannot be migrated: vda: the VM has no disk file to copy; "
+                   "sda (/i/os.iso): an image is not copied; eject it first")
+        self.assertEqual(error.args[0], english)
+        with translation.override("tr"):
+            self.assertNotEqual(str(error), english)
+            self.assertEqual(error.args[0], english)  # logs and the audit log stay English
+            self.assertIn("vda", str(error))
+
+    def test_a_job_keeps_number_values_for_their_formats(self):
+        from operations.utils import said, words
+        from vrtManager.util import OperationError
+
+        error = OperationError("Storage pool %(pool)s has %(free).1f GiB free; the clone needs %(size).1f GiB "
+                               "(the copied disks, plus %(percent)g%% of them, at least %(minimum)g GiB)",
+                               pool="default", free=1.25, size=3.0, percent=10, minimum=2)
+        self.assertEqual(words(said(error)), "Storage pool default has 1.2 GiB free; the clone needs 3.0 GiB "
+                                             "(the copied disks, plus 10% of them, at least 2 GiB)")
+
 
 if __name__ == "__main__":
     unittest.main()

vrtManager/tests/test_xml_safety.py

@@ -48,11 +48,11 @@ class TestXmlSafety(unittest.TestCase):
         wn.wvm = MagicMock()
 
         # Invalid direction
-        with self.assertRaises(ValueError):
+        with self.assertRaises(util.OperationError):
             wn.set_qos("lateral", 100, 200, 300)
 
         # Invalid numeric strings
-        with self.assertRaises(ValueError):
+        with self.assertRaises(util.OperationError):
             wn.set_qos("inbound", "not_a_number", 200, 300)
 
     def test_snapshot_xml_payload_is_escaped(self):