Add screen_stop()

Change-Id: Iac84231cfda960c4197de5b6e8ba6eb19225169a
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
Enable configuration of Identity API v3

* Default IDENTITY_API_VERSION to 'v2.0' in stackrc
* Set OS_IDENTITY_API_VERSION in openrc and strips the leading 'v'

Change-Id: I78e0ed5f1baaf236bf95ddf73be764072674d732
Merge branch 'screen-stop' into dt-test
Merge branch 'update-usb-tools' into dt-test