EFI hosts

If you have an EFI host but the image doesn't have the EFI modules
installed the grub-install command will fail in case the --target
argument is not set. The problem is that the grub-install script will
check whether the /sys/firmware/efi file exists or not to determine if
it's an EFI installation, but this value comes from the host, so this
patch will look for the /sys/firmware/efi file and will also check if
the EFI modules are installed in the image, if not set the --target to
a non-efi platform.

Change-Id: I4481b43e4a8fe4144be9c7eb9d9c618bbb2df21e
Merge "EFI hosts"