Move response validation schema's in sub folder

In order to move all negative test schema's to tempest/api_schema it's
needed to separate between response checking and request checking.

Change-Id: I27c03bbba3b559f9ef587cea5b4192f89b02dcf1
Partially-implements: bp api-schema-unification
diff --git a/tempest/services/compute/json/migrations_client.py b/tempest/services/compute/json/migrations_client.py
index beef5d2..f4abbb2 100644
--- a/tempest/services/compute/json/migrations_client.py
+++ b/tempest/services/compute/json/migrations_client.py
@@ -15,7 +15,7 @@
 import json
 import urllib
 
-from tempest.api_schema.compute import migrations as schema
+from tempest.api_schema.response.compute import migrations as schema
 from tempest.common import rest_client
 from tempest import config