PXE bare-metal provisioning helper server

a part of blueprint general-bare-metal-provisioning-framework.

Implement nova-baremetal-deploy-helper.

This service listens for HTTP requests from baremetal deploy ramdisk,
formats the remote disk and writes an image to it, as part of baremetal
PXE provisioning.

blueprint improve-baremetal-pxe-deploy shows how we plan to improve this
process.

Change-Id: I0a1b020cc5f81d49559acd4dcc781397a58e2c01
Co-authored-by: Mikyung Kang <mkkang@isi.edu>
Co-authored-by: David Kang <dkang@isi.edu>
Co-authored-by: Ken Igarashi <igarashik@nttdocomo.co.jp>
Co-authored-by: Arata Notsu <notsu@virtualtech.jp>
Co-authored-by: Devananda van der Veen <devananda.vdv@gmail.com>
Merge "PXE bare-metal provisioning helper server"