- fixed import of shim and grub efi modules. They are packaged
  as links to usr/lib/grub2/xxx-efi thus moving data from this
  directory will destroy the link target. We'd better copy it

- also allow integration of shim-opensuse key. If no Microsoft
  signed key is present we check if an opensuse key exists
- increased the vfat container image to be big enough to hold
  additional efi modules like the shim