Tweak the preceeding commit to:
* Add STARTTIME to the identifier to make it unique
* Use LOG_DIR
* Store the layer config in a more natural json format
* Drop '_' function prefixes
(From OE-Core rev: 173f59acf9722e2ef27fdd49c20f7d3d664917eb)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>