When I deploy linuxbridge-agent and enable tunneling,
the configuration of neutron isn't right. It lacks
the whole section [vxlan] to be properly configured.
Change-Id: Ib3bfe0f3445f466f4dbb36f7f0cb0d940114e7f6
Closes-Bug: #1481126
Related-Bug: #1524913
(cherry picked from commit c295bca61f)