Add option "disable creation jenkins instance"

[Alexander Charykov]

Feature create/edit/delete Jenkins instance should be able to be disallowed globally.

When this feature is disabled, create/edit/delete Jenkins instance button should be hidden.

Column actions also should be hidden.

[Igor Shishkin (teran)]

Frankly speaking it looks confusing since when are you seeing something like "disable_feature" you expect the feature to be disabled but some particular parts of it like in your case "some button".

[Alexander Lomski (aliaksandr-lomski)]

@acharykov Please clarify how this feature will be enabled/disabled. An extra option in settings.yaml?

[Alexander Charykov (acharykov)]

Yes, extra option in settings.yaml, with defaults in settings.py.

Also add this option to the docs.

[Fuel Devops McRobotson (fuel-devops-robot)]

Reviewed: https://review.fuel-infra.org/22394
Submitter: Alexander Charykov <email address hidden>
Branch: master

Commit: 8657e1e5cbcd3f17c6a0722a551cfff9e2b457de
Author: Alexander Lomski <email address hidden>
Date: Thu Jun 23 12:31:50 2016

New option in settings to disable Jenkins UI forms.

New boolean setting JENKINS_DISABLE_UI_FORMS is now available. If set to
true, all Jenkins CI create/edit/delete forms will be removed from UI.

Defaults to False in settings.py, but can be overridden in settings.yaml.

Closes-Bug: #1593413
Change-Id: I50101d05b1a6421ff9acfc13edbbd5a27d39b8b1