Remove incorrect Instance 1.18 relationship for PciDevice 1.2

Commit a55ea8c929 introduced a relationship
for Instance 1.18 to send PciDevice 1.2. That is problematic for people
doing commit-to-commit deployment of stable/kilo because upgrading your
conductor nodes before your computes will send back an unsupported
version 1.2. Just landing the version bump now means that all nodes will
tolerate a newer object, but conductors won't send it.

This change is not on master (because it doesn't make sense there).

Change-Id: Ibdfb0b52cc04e4055b83bad7c733e86bdc405d2a
Related-Bug: #1474074

nova/objects/instance.py

@@ -257,7 +257,12 @@ class Instance(base.NovaPersistentObject, base.NovaObject,
         'fault': [('1.0', '1.0')],
         'info_cache': [('1.1', '1.0'), ('1.9', '1.4'), ('1.10', '1.5')],
         'security_groups': [('1.2', '1.0')],
-        'pci_devices': [('1.6', '1.0'), ('1.15', '1.1'), ('1.18', '1.2')],
+        # NOTE(danms): We need to continue sending v1.1 whenever we're
+        # asked to backport a thing because our PciDeviceList was broken
+        # in kilo. That way we won't send a newer version than original
+        # kilo nodes can tolerate. See bug:
+        # https://bugs.launchpad.net/nova/+bug/1474074
+        'pci_devices': [('1.6', '1.0'), ('1.15', '1.1')],
         'numa_topology': [('1.14', '1.0')],
         'pci_requests': [('1.16', '1.1')],
         'tags': [('1.17', '1.0')],