remove_router_interface need to improve its validate to avoid 500 DBError

[watanabe.isao]

500 DBError should not be returned in a user operation.

[User operation]
========================
curl -i -X PUT -H "X-Auth-Token: $TOKEN" -H "Content-Type: application/json" http://192.168.122.201:9696/v2.0/routers/edff6799-7f1b-4d9e-bc8e-115cd22afd82/remove_router_interface -d '{"id":"edff6799-7f1b-4d9e-remove_router_interface"}'
HTTP/1.1 500 Internal Server Error
Content-Type: application/json; charset=UTF-8
Content-Length: 150
X-Openstack-Request-Id: req-31c11f44-73c4-47bf-bbc3-a3b0eb41148d
Date: Fri, 30 Jan 2015 06:30:26 GMT

{"NeutronError": {"message": "Request Failed: internal server error while processing your request.", "type": "HTTPInternalServerError", "detail": ""}}
========================

When subnet_id or port_id is not defined in the body of the above RESR API request, 400 Error should be returned.
However, the varidate for this is not enough and cause a 500 DB Error.

[TraceLog]
========================
2015-01-28 21:37:16.956 2589 ERROR neutron.api.v2.resource [req-c65b69cd-9a1b-4083-b85f-ea98030f5022 None] add_router_interface failed
2015-01-28 21:37:16.956 2589 TRACE neutron.api.v2.resource Traceback (most recent call last):
2015-01-28 21:37:16.956 2589 TRACE neutron.api.v2.resource File "/usr/lib/python2.6/site-packages/neutron/api/v2/resource.py", line 87, in resource
2015-01-28 21:37:16.956 2589 TRACE neutron.api.v2.resource result = method(request=request, **args)
2015-01-28 21:37:16.956 2589 TRACE neutron.api.v2.resource File "/usr/lib/python2.6/site-packages/neutron/api/v2/base.py", line 194, in _handle_action
2015-01-28 21:37:16.956 2589 TRACE neutron.api.v2.resource return getattr(self._plugin, name)(*arg_list, **kwargs)
2015-01-28 21:37:16.956 2589 TRACE neutron.api.v2.resource File "/usr/lib/python2.6/site-packages/neutron/db/l3_db.py", line 367, in add_router_interface
2015-01-28 21:37:16.956 2589 TRACE neutron.api.v2.resource 'tenant_id': subnet['tenant_id'],
2015-01-28 21:37:16.956 2589 TRACE neutron.api.v2.resource UnboundLocalError: local variable 'subnet' referenced before assignment
2015-01-28 21:37:16.956 2589 TRACE neutron.api.v2.resource
========================

[About fix]
A varidate like in add_router_interface should be good enough.
See add_router_interface is returning 400 correctly.
========================
curl -i -X PUT -H "X-Auth-Token: $TOKEN" -H "Content-Type: application/json" http://192.168.122.201:9696/v2.0/routers/139d6962-0919-444a-8ee4-8e47e35f054b/add_router_interface -d '{"router":{"name":"test_router"}}'
HTTP/1.1 400 Bad Request
Content-Type: application/json; charset=UTF-8
Content-Length: 134
X-Openstack-Request-Id: req-bca4b0ca-9e3a-4171-b783-ccc9a8c1cb80
Date: Thu, 29 Jan 2015 02:20:39 GMT

{"NeutronError": {"message": "Bad router request: Either subnet_id or port_id must be specified", "type": "BadRequest", "detail": ""}}
========================

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/151973

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/151973
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=405baef29ffae96bcf5410d5d93217f219a1bfda
Submitter: Jenkins
Branch: master

commit 405baef29ffae96bcf5410d5d93217f219a1bfda
Author: watanabe.isao <email address hidden>
Date: Fri Jan 30 17:56:24 2015 +0900

    Improve validate of remove_router_interface

    Improve validate of remove_router_interface as described in
    API referrence [1].

    [1]http://developer.openstack.org/api-ref-networking-v2.html
       PUT: /v2.0/routers/{router_id}/add_router_interface
       PUT: /v2.0/routers/{router_id}/remove_router_interface

    Also, add missing unit tests to cover a [add; delete] time
    [none; subnet id only; port id only; both ids] matrices.

    Change-Id: Ie4ddf61c4a4930a58d0817119566d2285a394065
    Closes-Bug: #1416308