Add a response header validation

Nova API sometimes returns important information in a response header,
and Tempest needs to check it for keeping the backward compatibility.
This patch adds the check for "create a server snapshot" API as the
sample.

Partially implements blueprint nova-api-attribute-test

Change-Id: I2441147ee050e7b818906aaa754dcec4480d8c18

tempest/api_schema/compute/v2/images.py

@@ -92,7 +92,17 @@ list_images = {
 }
 
 create_image = {
-    'status_code': [202]
+    'status_code': [202],
+    'response_header': {
+        'type': 'object',
+        'properties': {
+            'location': {
+                'type': 'string',
+                'format': 'uri'
+            }
+        },
+        'required': ['location']
+    }
 }
 
 delete = {

tempest/common/rest_client.py

@@ -593,10 +593,12 @@ class RestClient(object):
                 msg = ("The status code(%s) is different than the expected "
                        "one(%s)") % (resp.status, response_code)
                 raise exceptions.InvalidHttpSuccessCode(msg)
-            response_schema = schema.get('response_body')
-            if response_schema:
+
+            # Check the body of a response
+            body_schema = schema.get('response_body')
+            if body_schema:
                 try:
-                    jsonschema.validate(body, response_schema)
+                    jsonschema.validate(body, body_schema)
                 except jsonschema.ValidationError as ex:
                     msg = ("HTTP response body is invalid (%s)") % ex
                     raise exceptions.InvalidHTTPResponseBody(msg)
@@ -605,6 +607,15 @@ class RestClient(object):
                     msg = ("HTTP response body should not exist (%s)") % body
                     raise exceptions.InvalidHTTPResponseBody(msg)
 
+            # Check the header of a response
+            header_schema = schema.get('response_header')
+            if header_schema:
+                try:
+                    jsonschema.validate(resp, header_schema)
+                except jsonschema.ValidationError as ex:
+                    msg = ("HTTP response header is invalid (%s)") % ex
+                    raise exceptions.InvalidHTTPResponseHeader(msg)
+
 
 class NegativeRestClient(RestClient):
     """

tempest/exceptions.py

@@ -197,6 +197,10 @@ class InvalidHTTPResponseBody(RestClientException):
     message = "HTTP response body is invalid json or xml"
 
 
+class InvalidHTTPResponseHeader(RestClientException):
+    message = "HTTP response header is invalid"
+
+
 class InvalidContentType(RestClientException):
     message = "Invalid content type provided"