Expand service validation to work for Nova cells

In order to run the services tests on Nova cells the validation schema
needs to be adapted to handle the scoped region[!child]@<service_id>
format that cells uses.

Change-Id: I530f6635393af9310070cbb36b6e51eed1979ddb
diff --git a/tempest/api_schema/response/compute/services.py b/tempest/api_schema/response/compute/services.py
index fc42b89..6f361ef 100644
--- a/tempest/api_schema/response/compute/services.py
+++ b/tempest/api_schema/response/compute/services.py
@@ -22,7 +22,8 @@
                 'items': {
                     'type': 'object',
                     'properties': {
-                        'id': {'type': 'integer'},
+                        'id': {'type': ['integer', 'string'],
+                               'pattern': '^[a-zA-Z!]*@[0-9]+$'},
                         'zone': {'type': 'string'},
                         'host': {'type': 'string'},
                         'state': {'type': 'string'},