Code review comment for lp:~frankban/juju-quickstart/improve-unexpected-fields

Reviewers: mp+199270_code.launchpad.net,

Message:
Please take a look.

Description:
Improve unexpected fields handling.

Implement the UnexpectedField type. This is used
to handle unexpected key/value pairs found in
the environments.yaml file. The user will be able
to get rid of those fields just deleting their
values from in the interactive session.

Tests: `make check`.
No QA.

https://code.launchpad.net/~frankban/juju-quickstart/improve-unexpected-fields/+merge/199270

(do not edit description out of merge proposal)

Please review this at https://codereview.appspot.com/43380043/

Affected files (+142, -3 lines):
   A [revision details]
   M quickstart/models/envs.py
   M quickstart/models/fields.py
   M quickstart/tests/models/test_envs.py
   M quickstart/tests/models/test_fields.py