sstate: Add tweak to avoid multiple sstate stats messages

sstate: Add tweak to avoid multiple sstate stats messages

After the recent changes in bitbake to runqueue, we need to recheck sstate validity,
particularly in multiconfig builds where tasks have the same checksum.

Avoid printing summary messages in this case. Also avoid multiple events to toaster
which may not be expecting that at later points in the code.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>