This commit adds localboot support for uefi boot mode.
For uefi localboot, we switch partition table to gpt
and create a efi system partition. The efi system partition
is used later by bootloader (which is installed from
ramdisk).
Corresponding diskimage-builder change is here:
Idf7ac5987e14e1d31311834196ca7283deec15c6
Implements: blueprint local-boot-support-with-partition-images
Change-Id: I00ac31da325676ea4ea1ac4185f5ac3a52c5809a
da9ed8d0eb