After that for a while, one day I just came up with a idea: I read a book "Effective C++" and why not there is a book about "Effective Python"? So, here it is: http://www.effectivepython.com/
I wish I can find some time to walk through this book.
/etc/neutron/dhcp_agent.inifile and complete the following action:
[DEFAULT]section, enable the dnsmasq configuration file:
/etc/neutron/dnsmasq-neutron.conffile and complete the following action:
# pkill dnsmasq