classes/image: suppress log_check mechanism for warnings/errors logged through BitBake

classes/image: suppress log_check mechanism for warnings/errors logged through BitBake

If you printed a warning through bb.warn() / bbwarn or an error through
bb.error() / bberror, this was also being picked up by our log_check
mechanism that was designed to pick up warnings and errors printed by
other programs used during do_rootfs. This meant you saw not only the
warning or error itself, you saw it a second time through log_check,
which is a bit ugly. Use the just-added BB_TASK_LOGGER to access the
logger and add a handler that we can use to find out if any warning or
error we find in the logs is one we should ignore as it has already been
printed.

Fixes [YOCTO #8223].

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>