Return 200 when execute net-list-on-dhcp-agent api with incorrect agent_id

[Hirofumi Ichihara]

Neutron server return HTML code 200 when users execute net-list-on-dhcp-agent with incorrect agent_id.
Users expect to return HTML code 404.

I have already finished l3agent fix[1].

[1]: https://review.openstack.org/#/c/149531/

$ neutron agent-list
+--------------------------------------+--------------------+--------------------------------------+-------+----------------+---------------------------+
| id | agent_type | host | alive | admin_state_up | binary |
+--------------------------------------+--------------------+--------------------------------------+-------+----------------+---------------------------+
| 2343d3b3-c150-43e7-a9e8-8bf9425a1272 | DHCP agent | vagrant-ubuntu-trusty-64.localdomain | :-) | True | neutron-dhcp-agent |
| 3b9f0e0c-0c0d-4c7f-a057-b8ff2e0331e0 | Open vSwitch agent | vagrant-ubuntu-trusty-64.localdomain | :-) | True | neutron-openvswitch-agent |
| 41206a6f-8b8f-49e0-bc28-50b55b8df22e | Metadata agent | vagrant-ubuntu-trusty-64.localdomain | :-) | True | neutron-metadata-agent |
| 96ed22b2-c49e-4541-9214-5725aa469272 | L3 agent | vagrant-ubuntu-trusty-64.localdomain | :-) | True | neutron-l3-agent |
+--------------------------------------+--------------------+--------------------------------------+-------+----------------+---------------------------+

$ curl -i -X GET http://127.0.0.1:9696/v2.0/agents/hoge/dhcp-networks.json -H "User-Agent: python-neutronclient" -H "Accept: application/json" -H "X-Auth-Token: 95b769a44af64bf8a9ed769f05a83c8e"
HTTP/1.1 200 OK
Content-Type: application/json; charset=UTF-8
Content-Length: 16
X-Openstack-Request-Id: req-d0d02a71-cbb2-4190-8198-efe3087966cb
Date: Tue, 24 Feb 2015 15:37:36 GMT

{"networks": []}

[Oleg Bondarev (obondarev)]

Marking as higt as it's needed for API consistency

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/159046

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/159046
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=dc4268b8547ba9416c3c1de4fb41597ab9d5a6df
Submitter: Jenkins
Branch: master

commit dc4268b8547ba9416c3c1de4fb41597ab9d5a6df
Author: Hirofumi Ichihara <email address hidden>
Date: Wed Feb 25 18:02:35 2015 +0900

    Return 404 when executing net-list-on-dhcp-agent with invalid agent_id

    Neutron server returns HTTP code 200 when users execute
    net-list-on-dhcp-agent with invalid agent_id.
    Users expect HTTP code 404 to be returned.

    Change-Id: I41652a9bf4a81835abb6646ea870781472757623
    Closes-bug: 1425138