Comment 7 for bug 1746526

Reviewed: https://review.openstack.org/544370
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=232d766ed0f3cdbca9863d161dc81f7c0e4e50d7
Submitter: Zuul
Branch: stable/queens

commit 232d766ed0f3cdbca9863d161dc81f7c0e4e50d7
Author: Sławek Kapłoński <email address hidden>
Date: Thu Feb 1 12:59:02 2018 +0100

    Fix error message when duplicate QoS rule is created

    When user tries to create QoS rule which already exists in same
    QoS policy, only check if rule is duplicated was done on DB layer.
    Because of that, there was many retries of DB operations so user
    waits to response from Neutron server long time.
    Also error message returned from this DB related exception was not
    user friendly.

    This patch adds additional check of such duplicated rules before
    there is attempt to save new/updated rule in database so in case
    of error, response is send to user faster and it has proper
    message.

    Change-Id: I7d55df1eb931583c3dde064e073deb3e5479acc2
    Closes-Bug: #1746526
    (cherry picked from commit a91d84cfb44a9def517f2990d164b4972023709a)