reload_cfg doesn't work correctly

[cheng li]

class ProcessManager[1] is used to managed processes in neutron agents. The reload_cfg function is used to reload configuration by sending HUB signal to the target process. This may work for a linux system administrator, where she/he updates the config file and then sends HUP signal to reload.
But in openstack, this is a bit different. I have read the code about dnsmasq[2] and haproxy. The parameters and config files are generated by a callback function. This function generates config files and return the command(with parameters). Sending HUP signal doesn't change parameters, neither regenerate config files.

I would suggest another way to reload/restart process which makes sure the callback function is called.

[1] https://github.com/openstack/neutron/blob/8c59cfe98eb15f024b6c24312c0bf51af02a5dc3/neutron/agent/linux/external_process.py#L50
[2] https://github.com/openstack/neutron/blob/8c59cfe98eb15f024b6c24312c0bf51af02a5dc3/neutron/agent/linux/dhcp.py#L457-L458

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/626829

[Slawek Kaplonski (slaweq)]

This bug has had a related patch abandoned and has been automatically un-assigned due to inactivity. Please re-assign yourself if you are continuing work or adjust the state as appropriate if it is no longer valid.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Slawek Kaplonski (<email address hidden>) on branch: master
Review: https://review.openstack.org/626829
Reason: This review is > 4 weeks without comment, and failed Jenkins the last time it was checked. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and leaving a 'recheck' comment to get fresh test results.