incorrect definition of attributes in event model

[gordon chung]

the event model in sql backend incorrectly defines its backref attributes. it also references an undefined attribute in trait_type model

see: https://github.com/openstack/ceilometer/blob/master/ceilometer/storage/sqlalchemy/models.py#L376

trait_type does not have name attribute but has desc attr

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/101988

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/101988
Committed: https://git.openstack.org/cgit/openstack/ceilometer/commit/?id=aef1ed8b79904dacdd9364c7cf8654a9c71a86c5
Submitter: Jenkins
Branch: master

commit aef1ed8b79904dacdd9364c7cf8654a9c71a86c5
Author: Gordon Chung <email address hidden>
Date: Mon Jun 23 15:52:13 2014 -0400

    clean up event model

    - fix defined relationships so they are properly backref
    - fix trait_type __repr__ function to reference correct variable

    Change-Id: Id606025ca3e91c6e9b7da597f8cc3181caf4d4b7
    Closes-Bug: #1333399