Add tftp support for Fedora

switch to installing tftpd-hpa on ubuntu so both ubuntu and fedora are
using the same tftp implementation.

Fixes two problems with tftp on Fedora tftp-server 5.2-9
o tftp needs to be run as root so that it can set its userid to nobody,
  as tftp by default downgrades to nobody it should be safe to run as root.
  Prevents this error "cannot set groups for user nobody" which was
  preventing tftp from working.

o Add support for tftp requests that don't specify absolute paths, by remaping
  requests if they don't start in a /. I was seeing failed requests when they
  start in "pxelinux.cfg" i.e. don't start in "/tftpboot/", which was stalling
  the boot process.

Change-Id: I7ce923bead605486c310b08697942f7f868709b0
Merge "Add tftp support for Fedora"