dhcpv6-stateless cause dhcp _generate_opts_per_subnet fail

[ZongKai LI]

ipv6 subnet with dhcpv6_stateless address mode cause KeyError in https://github.com/openstack/neutron/blob/master/neutron/agent/linux/dhcp.py#L895 , when force_metadata is configured as True.

2016-09-19 06:55:44.211 ERROR neutron.agent.dhcp.agent [-] Unable to enable dhcp for c0eea6e2-f98d-48b9-aab0-67113a82a70e.
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent Traceback (most recent call last):
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent File "/opt/stack/neutron/neutron/agent/dhcp/agent.py", line 114, in call_driver
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent getattr(driver, action)(**action_kwargs)
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent File "/opt/stack/neutron/neutron/agent/linux/dhcp.py", line 213, in enable
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent self.spawn_process()
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent File "/opt/stack/neutron/neutron/agent/linux/dhcp.py", line 425, in spawn_process
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent self._spawn_or_reload_process(reload_with_HUP=False)
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent File "/opt/stack/neutron/neutron/agent/linux/dhcp.py", line 434, in _spawn_or_reload_process
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent self._output_config_files()
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent File "/opt/stack/neutron/neutron/agent/linux/dhcp.py", line 467, in _output_config_files
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent self._output_opts_file()
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent File "/opt/stack/neutron/neutron/agent/linux/dhcp.py", line 845, in _output_opts_file
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent options, subnet_index_map = self._generate_opts_per_subnet()
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent File "/opt/stack/neutron/neutron/agent/linux/dhcp.py", line 895, in _generate_opts_per_subnet
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent subnet_dhcp_ip = subnet_to_interface_ip[subnet.id]
2016-09-19 06:55:44.211 TRACE neutron.agent.dhcp.agent KeyError: u'7e086056-521a-4d91-b2a7-6d1b3fffb49b'

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/372259

[OpenStack Infra (hudson-openstack)]

Change abandoned by ZongKai LI (<email address hidden>) on branch: master
Review: https://review.openstack.org/372259