unify indention

unify indention to four spaces
use grub2-probe to get device map

We get the translated os device to grub device mapping thru the
grub2-probe result. By means of this new method we can avoid the mess of
requirement to create file /boot/grub2/device.map which is intented for
perl bootloader to work but is not necessary for grub2.

This fixes the integration issue with kiwi as it couldn't provide such
device map like yast. (bnc#804065)
clean up unused functions and variables

clean up unused variable $md_discs and UnixDev2GrubDev() function
remove floppy in device map

Remove floppy in device map to fix long time accessing it. As we
don't specify grub device but os device for installation, thus that
entry not used for translate os device any longer. (bnc#796917).
fix grub2-set-default error during installation

During installation we have "/usr/sbin/grub2-set-default: No such file
or directory" error although the installation finished successfully. We
fix this misleading message by moving it to the update and initialize
fuction which grub2 package must has been installed when invoked.