Method to generate PXE options for Neutron ports

Add a new method to generate the structure containing the PXE
bootfile-name, server-ip-address, and tftp-server information.
This information will be used to provide Neutron DHCP options
to set up the PXE booting of nodes. This patch does not actually pass
the data to Neutron, however.

Change-Id: Iadf5b803bb5a5465fc2adcb94fa3fd2a756340be
Merge "Method to generate PXE options for Neutron ports"