update_bootloaders: use uuids for legacy boot.
update_bootloaders: use uuids for legacy boot.

BUG=chromium-os:14127,chromium-os:17184
TEST=Adhoc
Build a regular image (for Alex) and boot it on a Dogfood machine (which uses
legacy boot). Check dmesg for PARTUUID. Unpack partitions, mount partition 12,
and check for root=PARTUUID= in /efi/grub/grub.cfg (it should be there instead
of root=/dev/$linuxpart).

Change-Id: Ie403632f227d514a5876f8338afa4ad80708ed55
Signed-off-by: Elly Jones <1693f95ea06ee6d7b2276cb599c3f4f33a951d9c@chromium.org>
Reviewed-on: http://gerrit.chromium.org/gerrit/5668
Reviewed-by: Will Drewry <72416dde44ea762d19e3a7a555e3b59ce98f8eea@chromium.org>

bcwaldon/coreos-scripts,nicescale/scripts,marineam/coreos-scripts,bcwaldon/coreos-scripts,mjg59/scripts,fivethreeo/scripts,glevand/coreos--scripts,endocode/scripts,nicescale/scripts,mjg59/scripts,crawford/scripts,gtank/scripts,smilart/scripts,marineam/coreos-scripts,mischief/scripts,smilart/scripts,vmware/coreos-scripts,zhang0137/scripts,marineam/coreos-scripts,BugRoger/scripts,gtank/scripts,sigma/coreos-scripts,crawford/scripts,sigma/coreos-scripts,zhang0137/scripts,mjg59/scripts,vmware/coreos-scripts,crawford/scripts,fivethreeo/scripts,mischief/scripts,mischief/scripts,coreos/scripts,trnubo/scripts,trnubo/scripts,glevand/coreos--scripts,endocode/scripts,andrejro/coreos--scripts,andrejro/coreos--scripts,bcwaldon/coreos-scripts,sigma/coreos-scripts,fivethreeo/scripts,coreos/scripts,andrejro/coreos--scripts,zhang0137/scripts,BugRoger/scripts,endocode/scripts,nicescale/scripts,smilart/scripts,vmware/coreos-scripts,BugRoger/scripts,gtank/scripts,trnubo/scripts