Bug#687921: Make os-prober to support efi loaders

[Michael Chang <mchang@suse.com>]

Package: os-prober
Version: 1.49

Downstream Bug: 
https://bugzilla.novell.com/show_bug.cgi?id=775614

The os-prober didn't work on efi firmware that each operation system
loader is in the efi system partition rather than the boot sector.

It remains using the legacy approach somehow and one of the consequence
is that grub2 uses wrong stanza when trying to bootstrappe windows
under UEFI.

It uses

  chainloader +1

A correct one should be something like this

  chainloader (${root})/efi/Microsoft/Boot/bootmgfw.efi

Besides, I'd like chainloader be used as a generic way for any other
distributions in UEFI mode. Compared to probing bootloader's config
to know how to load kernel and initrd, the chainloader logic under the
UEFI mode would much simplify and more reliable IMHO. At least for me
that foregin OS config's change is independent and not influence it's
booting ..

The could make grub2 work in UEFI mode more like other utilites like
rEFIt or rEFInd ..

I know the testing version is a little stale, so please feel free to
close if the support has been done or working in progress. :)

Thanks,
Michael