Make checking of Trust existence more DRY

[Lin Hua Cheng]

The code for checking if Trust exists is duplicated all over the controller:

if not trust:
    raise exception.TrustNotFound(trust_id=trust_id)

https://github.com/openstack/keystone/blob/master/keystone/trust/controllers.py#L77-L78

to make it more DRY, remove the check in controller and move it the driver

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/173158

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/173158
Committed: https://git.openstack.org/cgit/openstack/keystone/commit/?id=deca783d99577283ba30a376a4f165c005d03573
Submitter: Jenkins
Branch: master

commit deca783d99577283ba30a376a4f165c005d03573
Author: lin-hua-cheng <email address hidden>
Date: Mon Apr 13 20:12:56 2015 -0700

    Checking if Trust exists should be DRY

    Instead of duplicating the check for Trust existence in the
    controller, move the check to the driver.

    Change-Id: Id576ebe9922a70047b8276f372854e086295b6c4
    Closes-Bug: #1443721

[Dolph Mathews (dolph)]

Given that this has no end user impact (and thus does not belong in release notes), changing from Wishlist to Low.