Cannot create symlink

[MathiasRenner]

As of now, in the last build step this command throws an error:
https://github.com/hypriot/image-builder-bananapi/blob/master/build.sh#L88:L96

... saying:

*stdin*:7: libguestfs: error: tar_in: tar subcommand failed on directory: /boot: tar: ./zImage: Cannot create symlink to 'vmlinuz-4.3.3-sunxi': Operation not permitted