Fix retrieving inexistent queue errors when using boto3.

Handle 404 errors when trying to retrieve a SQS queue that does not
exist. Add get_queue and get_inexistent_queue tests for boto3.

moto/sqs/responses.py

@@ -50,6 +50,12 @@ class SQSResponse(BaseResponse):
 
         return visibility_timeout
 
+    def call_action(self):
+        status_code, headers, body = super(SQSResponse, self).call_action()
+        if status_code == 404:
+            return 404, headers, ERROR_INEXISTENT_QUEUE
+        return status_code, headers, body
+
     def create_queue(self):
         queue_name = self.querystring.get("QueueName")[0]
         queue = self.sqs_backend.create_queue(queue_name, visibility_timeout=self.attribute.get('VisibilityTimeout'),
@@ -438,3 +444,13 @@ ERROR_TOO_LONG_RESPONSE = """<ErrorResponse xmlns="http://queue.amazonaws.com/do
 </ErrorResponse>"""
 
 ERROR_MAX_VISIBILITY_TIMEOUT_RESPONSE = "Invalid request, maximum visibility timeout is {0}".format(MAXIMUM_VISIBILTY_TIMEOUT)
+
+ERROR_INEXISTENT_QUEUE = """<ErrorResponse xmlns="http://queue.amazonaws.com/doc/2012-11-05/">
+    <Error>
+        <Type>Sender</Type>
+        <Code>AWS.SimpleQueueService.NonExistentQueue</Code>
+        <Message>The specified queue does not exist for this wsdl version.</Message>
+        <Detail/>
+    </Error>
+    <RequestId>b8bc806b-fa6b-53b5-8be8-cfa2f9836bc3</RequestId>
+</ErrorResponse>"""