image-vmdk: Create image_vmdk class and setup image and image_types to use it

image-vmdk: Create image_vmdk class and setup image and image_types to use it

This creates a new image_vmdk class similar to live. The image_vmdk
class needs to have a hddimg created by the image-live class, so it
inherits it directly.

The changes to image_types is to ensure that both live and vmdk images
get the ext3 tools and dependencies.

(From OE-Core rev: aa961e112b07d42c272e01f2d69f3c139e9ae70f)

Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>