Allow change disk order for grub2

Fix YaST doesn't allow to change disk order when grub2 is choosen as
bootloader (bnc#785569)
Remove grub2 under developing warning

Remove grub2 is still under develope and test warning after user choosed
it. (bnc#780637)
Make better grub2 install summary

Make better grub2 install summary as much information as we used to have
for legacy grub.
Make GRUB_DISTRIBUTOR with product version

First the Product::name returns version on running systems but not on
the installation system. We have to ensure that the version is specified
to GRUB_DISTRIBUTOR anyway.

Without the version, EFI boot menu would be added as "openSUSE" for all
versions and reference same bootloader path. This casues problem on
multiple version installation.

This fixes EFI boot menu entry cannot be chosen and multiple openSUSE
installations will overwrite it (bnc#796514).
Merge pull request #12 from WenhuaChang/master

Some bug fixing and improve grub2's summary