switch cloud images permanently to grub2
The main reason for cloud to use extlinux is the size of deps being
pulled in by grub2-tools. This will be fixed in F-26 with the ability
to use grub2/grub2-efi without the tools package and it's deps fixing
this issue for good. There will no doubt need to be be some tweaking
required here.
We need grub2 in cloud images for non x86 as well as for the increasing
x86 cloud platforms that require the support of uEFI which extlinux
doesn't support.
Signed-off-by: Peter Robinson <pbrobinson@fedoraproject.org>