Update default Nova API version to 2.53(Pike)

Services are now identified by uuid instead of database id to ensure
uniqueness across cells.
GET /os-services returns a uuid in the id field of the response
from API microversion 2.53(maximum in Pike)

This patch set updates default Nova API version to 2.53.

Change-Id: Ib9fefb794eda3c9e75c6a2f5cfdb0e682b8955f3
Closes-Bug: #1709544

watcher/decision_engine/model/element/node.py

@@ -33,7 +33,7 @@ class ServiceState(enum.Enum):
 class ComputeNode(compute_resource.ComputeResource):
 
     fields = {
-        "id": wfields.NonNegativeIntegerField(),
+        "id": wfields.StringField(),
         "hostname": wfields.StringField(),
         "status": wfields.StringField(default=ServiceState.ENABLED.value),
         "state": wfields.StringField(default=ServiceState.ONLINE.value),