Comment # 4 on bug 1172390 from Josef Reidinger

for me it looks like system ruby version is not switched. Bootloader has
dependency on cfa grub2

https://github.com/yast/yast-bootloader/blob/master/package/yast2-bootloader.spec#L36

Can you please inspect in openqa image what is output of 

ls -l /usr/lib*/ruby/gems/*/gems/cfa_grub2-*/