Fix flavor swap default value for compute microversion 2.75

As of microversion 2.75 default return value of swap in the response of
create_flavor is 0 instead of empty string, so this is to fix
test_create_list_flavor_without_extra_data for microversion 2.75.

https://docs.openstack.org/api-ref/compute/?expanded=create-flavor-detail#create-flavor

Change-Id: Ib086f9977f838cf884c7324b7b6eead698adaa9e
diff --git a/tempest/api/compute/admin/test_flavors.py b/tempest/api/compute/admin/test_flavors.py
index f42f53a..d6b6b7e 100644
--- a/tempest/api/compute/admin/test_flavors.py
+++ b/tempest/api/compute/admin/test_flavors.py
@@ -107,7 +107,10 @@
         """
         def verify_flavor_response_extension(flavor):
             # check some extensions for the flavor create/show/detail response
-            self.assertEqual(flavor['swap'], '')
+            if self.is_requested_microversion_compatible('2.74'):
+                self.assertEqual(flavor['swap'], '')
+            else:
+                self.assertEqual(flavor['swap'], 0)
             self.assertEqual(int(flavor['rxtx_factor']), 1)
             self.assertEqual(flavor['OS-FLV-EXT-DATA:ephemeral'], 0)
             self.assertEqual(flavor['os-flavor-access:is_public'], True)