compute update do unused update of RT when set instance to ERROR

[jichenjc]

we have function _set_instance_error_state in compute manager
 it will update the RT if the instance is set to ERROR , actually
nothing changed except the instance state .
so we don't need to do so, use _set_instance_obj_error_state will be fine

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/181426

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/181426
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=e4b249c988da38552adfb9c1025406d17bbb4316
Submitter: Jenkins
Branch: master

commit e4b249c988da38552adfb9c1025406d17bbb4316
Author: jichenjc <email address hidden>
Date: Wed May 6 18:42:49 2015 +0800

    Don't update RT status when set instance to ERROR

    nova will set instance status to ERROR then call RT update
    after that, it's not needed becaues RT is used to track instance
    state and check whether it's new created or deleted.
    Update instance to ERROR in DB should be fine.

    Change-Id: I550caf55d32931de1dac43862af15323c18a4431
    Closes-Bug: 1453170