dhcp agent uses root_helper setting from dhcp_agent.ini and quantum.conf

Generally, the dhcp agent uses the root_helper setting from the [AGENT] section of /etc/quantum/quantum.conf. However, there are a couple of places where it uses root_helper from the [DEFAULT] section of /etc/quantum/dhcp_agent.ini. I discovered this problem after I followed the latest openstack installation guide for ubuntu. I saw messages like this in the dhcp_agent log file:

Command: ['sudo', 'ip', 'netns', 'exec', 'qdhcp-0ad970b3-4f9e-445c-8b87-018d74fd02f2', 'quantum-ns-metadata-proxy', '--pid_file=/var/lib/q
uantum/external/pids/0ad970b3-4f9e-445c-8b87-018d74fd02f2.pid', '--network_id=0ad970b3-4f9e-445c-8b87-018d74fd02f2', '--state_path=/var/li
b/quantum', '--metadata_port=80', '--debug', '--verbose', '--log-file=quantum-ns-metadata-proxy0ad970b3-4f9e-445c-8b87-018d74fd02f2.log',
'--log-dir=/var/log/quantum']
Exit code: 1
Stdout: ''
Stderr: 'sudo: no tty present and no askpass program specified\nSorry, try again.\nsudo: no tty present and no askpass program specified\nSorry, try again.\nsudo: no tty present and no askpass program specified\nSorry, try again.\nsudo: 3 incorrect password attempts\n'
2013-05-08 06:43:40 ERROR [quantum.agent.dhcp_agent] Unable to sync network state.
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/quantum/agent/dhcp_agent.py", line 155, in sync_state
    self.refresh_dhcp_helper(network_id)
  File "/usr/lib/python2.7/dist-packages/quantum/agent/dhcp_agent.py", line 209, in refresh_dhcp_helper
    return self.enable_dhcp_helper(network_id)
  File "/usr/lib/python2.7/dist-packages/quantum/agent/dhcp_agent.py", line 188, in enable_dhcp_helper
    self.enable_isolated_metadata_proxy(network)
  File "/usr/lib/python2.7/dist-packages/quantum/agent/dhcp_agent.py", line 329, in enable_isolated_metadata_proxy
    pm.enable(callback)
  File "/usr/lib/python2.7/dist-packages/quantum/agent/linux/external_process.py", line 55, in enable
    ip_wrapper.netns.execute(cmd)
  File "/usr/lib/python2.7/dist-packages/quantum/agent/linux/ip_lib.py", line 407, in execute
    check_exit_code=check_exit_code)
  File "/usr/lib/python2.7/dist-packages/quantum/agent/linux/utils.py", line 61, in execute
    raise RuntimeError(m)

I'm going to submit a patch in a moment.