Switch to using a dedicated TFTPd for baremetal.

We currently use dnsmasq to provide TFTP when booting baremetal nodes,
but that becomes redundant when we switch to using neutron's DHCP
agent. Instead we need a dedicated TFTPd, and we can use that with
dnsmasq by disabling dnsmasq's built-in TFTPd, giving a consistent
setup.

Change-Id: I985fff9a3dded1b0dffe82fa5d48009441777733
Set the seed nodes host name to 'seed'.

This makes more sense than calling it 'ubuntu'.

Note: This will require an associated incubator change which
I will push momentarily.

Change-Id: I69093aaf8ecd0ff38e5b67aaf67886120a581a80
Merge "Set the seed nodes host name to 'seed'."
Merge "Switch to using a dedicated TFTPd for baremetal."