fix(appsettings): settings take only the values the panel can use

The Settings page saved whatever was posted, and some lists offered
values the panel cannot use:

- Quota Debug could not be turned off: "False" is a non-empty text and
  counted as on.
- VM Clone Name Prefix showed as a True/False list, so no prefix could
  be typed, and touching it set the prefix to True.
- Disk SCSI Controller listed " lsilogic" with a space, never shown as
  chosen, and virtio-blk, which is no SCSI controller.
- VM Machine Type listed x86_64, an architecture; VM CD-ROM Device
  listed virtio, a bus a CD-ROM cannot use.
- Logs per Page and Disk Owner UID/GID are read with int(): a letter
  broke the logs page and VM create.

A migration fixes the lists and moves a value they no longer offer to
the default (the clone prefix keeps its text). A listed setting now
takes one of its choices, and every number setting a whole number in
its range, checked before it is saved.

instances/tests/test_quota.py

@@ -111,6 +111,19 @@ class QuotaTests(TestCase):
         Instance.objects.filter(pk=vm.pk).update(is_template=True)
         self.assertEqual(self.check(0, 2, 0, 0), ("", 3))
 
+    def test_the_numbers_show_only_with_quota_debug_on(self):
+        # the setting is the text "True" or "False": "False" turns them off
+        from appsettings.models import AppSettings
+
+        for i in range(5):
+            self.own(self.up, i)
+        for value, expected in (("True", "instance (6 > 5)"), ("False", "instance")):
+            with self.subTest(value=value):
+                AppSettings.objects.filter(key="QUOTA_DEBUG").update(value=value)
+                get_settings()
+                with patch.object(Compute, "status", True), patch("instances.utils.wvmInstance", side_effect=vm_reader()):
+                    self.assertEqual(check_user_quota(self.user, 1, 0, 0, 0), expected)
+
 
 class QuotaViewTests(TestCase):
     """The resize views turn the result into a message and charge only what changes."""