Allow to configure root_helper_daemon

[Giuseppe Petralia]

Use ‘sudo neutron-rootwrap-daemon /etc/neutron/rootwrap.conf’ to run rootwrap in “daemon mode” which has been reported to improve performance at scale. For more information on running rootwrap in “daemon mode”, see:

https://docs.openstack.org/oslo.rootwrap/latest/user/usage.html#daemon-mode

It would be nice to have that option on the charm to improve performances of neutron agents.

This will need to modify both neutron.conf [agent] section and neutron sudoers.d file.

Ref. https://docs.openstack.org/neutron/latest/configuration/neutron.html#agent.root_helper_daemon