Unhelpful error when modifying security group fails

[Chris St. Pierre]

When modifying instance security groups, Horizon catches all exceptions and reraises a simple, dumb Exception with the message:

    Failed to modify %d instance security groups.

That's useless enough, but since it reraises Exception, it has no hope of being caught further downstream and reported meaningfully to the user.

To see this in action, attempt to modify the security groups of a suspended instance. Nova returns a decent error to Horizon, but Horizon returns a useless error to the user.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/99912
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=43248863d0a8099ace90df27af2f0ac269b707b6
Submitter: Jenkins
Branch: master

commit 43248863d0a8099ace90df27af2f0ac269b707b6
Author: Chris St. Pierre <email address hidden>
Date: Fri Jun 13 07:24:08 2014 -0400

    Raise sane error when failing to modify security group

    Horizon catches and propagates recoverable exceptions back to the
    user. This code previously caught all exceptions and then raised
    Exception (with an unhelpful message), which Horizon propagated as an
    even less helpful message. By raising the error as a
    novaclient.exception.ClientException, we give Horizon a fighting
    chance of passing a useful (but sanitized) error message to the user.

    This changes the message the user sees from:

    Error: There was an error submitting the form. Please try again.

    To:

    Error: Unable to modify instance "test10".
    Error: Failed to modify 1 instance security groups

    The error condition can be simulated by trying to modify security
    groups on a suspended instance.

    Closes-Bug: #1329888
    Change-Id: I38d9977d6d20dfeddbb77b1a7e63e74597bf7331