Drop grub1

![Warning](https://raw.githubusercontent.com/yast/yast-theme/master/icons/hicolor/32x32/apps/msg_warning.png) **NOTE: merge this after creating the maintenance branch for SLE-12 and after switching Jenkins to use the new branch**
this is not goal of this PR, I want just drop grub1, pass openQA and then start with refactoring. Otherwise I spend ages just with refactoring, which bootloader really deserve.