DRY switcher

big improvement from F to A :+1: 
https://codeclimate.com/github/yast/yast-bootloader/compare/switcher_cleanup
OK. So it could be made more readable with
```ruby
recheck = false
functions = get_functions(BootCommon.getLoaderType(recheck))
```

or even by using [`Bootloader.getLoaderType()`](https://github.com/yast/yast-bootloader/blob/71209a82af73445550724d8d44630d4835dbb653/src/modules/Bootloader.rb#L561) (but module dependencies might prevent that).