build-appliance-image: Allow SRCREV to be overriden
This will allow use to automagically set the SRCREV for builds on the
autobuilder. It will still require manual updating for releases.
(From OE-Core rev: 1b4781e5c6eee234fcf57dd53d5167b31d81a482)
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Scott Garman