x11-sato-image: renamed poky-image-base as this image is not related to any of Poky...

In Poky we have:
- poky-image-base
- poky-image-sato
and x11-sato-image is not any of them. Developers are free to create any images
but their naming should be consistent with other images.

diff --git a/packages/images/poky-base-image.bb b/packages/images/x11-sato-image.bb
similarity index 100%
rename from packages/images/poky-base-image.bb
rename to packages/images/x11-sato-image.bb