impossible to modify template loaders when customizon horizon

[Yves-Gwenael Bourhis]

When customizing horizon as per:
http://docs.openstack.org/developer/horizon/topics/customizing.html#modifying-existing-dashboards-and-panels

we need to modify TEMPLATE_LOADERS in local settings, usually horizon customizers need:
https://pypi.python.org/pypi/django-apptemplates/

To extend original templates with ease

Since this patch:
https://review.openstack.org/#/c/281976/

horizon simply nukes any attempt to modify TEMPLATE_LOADERS because they are redifined after loading the local_settings. therefore customizing horizon is impossible without doing horizon code intrusion.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/304067

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/304067
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=17176d06173133a7e59432fdbd46af30e44c20d3
Submitter: Jenkins
Branch: master

commit 17176d06173133a7e59432fdbd46af30e44c20d3
Author: Yves-Gwenael Bourhis <email address hidden>
Date: Mon Apr 11 13:40:44 2016 +0200

    Template loaders defined before local settings

    TEMPLATE_LOADERS was defined after loading local_settings.py and was sqashing
    any attempt to customize the template loaders.
    This patch adds CACHED_TEMPLATE_LOADERS, ADD_TEMPLATE_LOADERS and a doc
    defining how to use them in order to ease customization process.

    Change-Id: I2544529ee965ef01c6ac4973056801ebee50be6d
    Closes-Bug: #1568764

[Davanum Srinivas (DIMS) (dims-v)]

This issue was fixed in the openstack/horizon 10.0.0.0b1 development milestone.