Deploy new images in validation farm

Status:
[pwlars, Apr 25] Postponing vexpress as it can be flaky and requires network booting at the moment, which is supposed to be resolved by a future uboot. Getting working boot config for u8500 and orion should still be doable in the next few weeks though.
Postponed ux500 because we are targeting snowball instead at STE's recommendation, and we don't have those boards yet.
[pwlars, May 16] Postponing Orion as we still have boot-on-poweron problem and other issues preventing it from being completely automated yet.

Work items:
Write scripts to find/download latest rootfs and hwpack: DONE
Investigate using l-m-c for better generic image deployment: DONE
Write scripts to run linaro-media-create generate image, extract filesystem tarballs: DONE
Add support for running linaro-media-create in schroot: DONE
Image/hwpack download function with local caching: DONE
Setup an image cache for linaro snapshot images on control node: DONE
Write simple function for returning a pyexpect object for interacting with the serial console on a given board: DONE
Create script for formatting partitions on the board, and extracting root/boot tarballs: DONE
Create function to boot test image on beagleXM: DONE
Create function to boot test image on Panda: DONE
Create function to boot test image on babbage: DONE
Create function to boot test image on ux500: POSTPONED
Create function to boot test image on vexpress: POSTPONED
Create function to boot test image on orion: DONE
Create dead board recovery function: DONE