Update USB boot tools

* update tools/get_uec_image.sh for precise and proxy operation
* add cleanup to tools/warm_apts_and_pips_for_uec.sh, remove pip download
* run tools/warm_apts_and_pips_for_uec.sh as root
* update tools/build_ues_ramdisk.sh for precise; add exec sudo
* update tools/build_usb_boot.sh to use $DEST

Change-Id: If3cc0a8973805f0376dfce2bcbb75082f2e039d3
Add screen_stop()

Change-Id: Iac84231cfda960c4197de5b6e8ba6eb19225169a
Periodic formatting cleanup

This is the semi-irregular comment and docs cleanup.

No functional changes should be here although some code is moved in a
small attempt to sort functions and get things where they need to be.

Change-Id: Ib4a3e2590c6fbd016c391acc7aef6421e91c0dca
Merge branch 'screen-stop' into dt-test
Merge branch 'update-usb-tools' into dt-test