Support flask 0.11

[rafaelcaricio]

Fixes #239
Replaces #237

Simple change makes Connexion compatible with Flask 0.11

Since the Flask 0.11 the supported error handlers are the ones that have specific exception in werkzeug. The HTTP error code 402 is not supported by Werkzeug so we cannot use it in tests.

Changes proposed in this pull request:

• Calls properly the add_error_handler funcion from Flask App
• Fix tests

[coveralls]

Coverage remained the same at 100.0% when pulling e387118 on rafaelcaricio:support-flask-0.11 into a83598d on zalando:master.

[jmcs]

Don't forget to update the requirements.

[rafaelcaricio]

@jmcs We still support 0.10.1 so there is no reason to update our requirements since it uses Flask>=0.10.1.

[rafaelcaricio]

@jmcs also there is a test env to guarantee that we run tests in the version 0.10.1 of Flask.

[jmcs]

👍

[hjacobs]

👍