Add retry_after only to exceptions supporting it

Having retry_after in HTTP response header for 403 status code caused
client to fail with TypeError exception about unexpected keyword
argument. This is related to bug in nova-api. To prevent this kind of
client problems in the future patch adds check to from_response
function to pass retry-after header only to classes that inherit
from RetryAfterException and regression unit tests.

Change-Id: I6bfc8b33eb591d30b3c647397b11100094718e13
Closes-Bug: 1365251
Merge "Add retry_after only to exceptions supporting it"