plugin panels cannot add exceptions

[Rob Raymond]

Currently only dashboard plugins can register what exceptions are treated as unknown, recoverable or unauthorized by horizon's handle exceptions.
It seems that panels may also need the ability to register what exceptions need to be handled.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/101650

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/101650
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=0f5a7b33dcae927dfc653d914912ef8a7c777771
Submitter: Jenkins
Branch: master

commit 0f5a7b33dcae927dfc653d914912ef8a7c777771
Author: Rob Raymond <email address hidden>
Date: Fri Jun 20 14:44:10 2014 -0600

    Allow panel plugins to use ADD_EXCEPTIONS and UPDATE_HORIZON_CONFIG

    This change allows panel plugins tell horizon which exceptions to treat as recoverable.
    Previously only dashboard plugins were allowed to register exceptions.
    Since there are now more settings that are common than specific to pluggable use case,
    the doc was restructured to describe in general pluggable settings and then describe
    the specific use cases.

    Change-Id: I013ece33ae2b979e92be9c7ba50182025a1ecb91
    Closes-bug: #1332688