Fixed EC2 no more mkinitrd

- modify the way we create an EC2 image
  + prior to this change the initrd for an EC2 image was created with mkinitrd
    as mkinitrd changes got introduced that require a live root filesystem
    using mkinitrd is no longer feasible. The same situation applies as things
    move to dracut
  + we now use a kiwi generated initrd for a vmx image type, and modify
    specific files (menu.lst, bootloader setup, inittab) in the image
    to make the image ec2 specific
  + this change requires the use of different EC2 akis, we need to use an aki
    designated for a partitioned image hd00 designation
  + using the VMX build type creates a partitioned image, thus we need to
    use a different device mapping when creating the ec2-bundle, use
    ami=sda instead of ami=sda1
- update the unit tests to reflect the changes
- EC2 XML validation now checks that the image type is VMX instead of a
  filesystem
  + this is somewhat superfluous as it is more intuitive to build an EC2
    image as VMX. However as the previous type requirement was a file system
    we want to catch this and let people know if the config is incorrect.
- Use GPT partition for EC2
  + Amazon is transitioning to expecting GPT, thus we need to follow suit
- update the 12.2 and 12.3 examples to reflect the new build type settings
  for ec2 images
- add an ec2 example for 13.1