overview-manual, mega-manual: Updated the sdk figure

Added the manifest files to the figure and the associated variables.
Also added the test files.

(From yocto-docs rev: cfba55462d1c37ef2ff6454890da64a40f9c3607)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>