NeutronV2 API is missing associate method.

[Leandro Ignacio Costantino]

Using nova network-associate-host w/neutron an error is returned because associate method is not defined in NeutronV2API.

Also, NotImplementedError is not being handled.

----
2014-03-17 09:12:15.783 TRACE nova.api.openstack action_result = self.dispatch(meth, request, action_args)
2014-03-17 09:12:15.783 TRACE nova.api.openstack File "/opt/stack/nova/nova/api/openstack/wsgi.py", line 1070, in dispatch
2014-03-17 09:12:15.783 TRACE nova.api.openstack return method(req=request, **action_args)
2014-03-17 09:12:15.783 TRACE nova.api.openstack File "/opt/stack/nova/nova/api/openstack/compute/contrib/networks_associate.py", line 60, in _associate_host
2014-03-17 09:12:15.783 TRACE nova.api.openstack self.network_api.associate(context, id,
2014-03-17 09:12:15.783 TRACE nova.api.openstack AttributeError: 'API' object has no attribute 'associate'
2014-03-17 09:12:15.783 TRACE nova.api.openstack
-------------------------

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/80962

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/80962
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=f349b7c80670f1993fb35bfd1d2bbd3ccbe16fef
Submitter: Jenkins
Branch: master

commit f349b7c80670f1993fb35bfd1d2bbd3ccbe16fef
Author: Leandro I. Costantino <email address hidden>
Date: Mon Mar 17 09:09:04 2014 -0300

    Catch NotImplementedError on Network Associate

    When trying to associate/disassociate a network both for project/host
    using neutron a 500 error is returned because the "associate" method is
    not even defined in neutronv2 api.

    The changes are:
       * Add missing associate method to neutronv2 api and raise
         NotImplementedError
       * Catch NotImplementedError on the API to return the proper error
         code on network associate/disassociate operations.
       * Catch NotImplementedError on os_network when associating a network

    Closes-Bug: #1293539
    Change-Id: I75b980500f0f171b065b7606baf201ab89848e92