Currently exceptions that happen in pool commands are ignored. Any errors
would be printed on the console but everything else is silent.
Switch to use pool.map_async which allows for an error_callback which
we can use to detect exceptions and make sure these errors are handled.
(From OE-Core rev: 7f2f9b3ff011b340b5d23bb7c47b12c357dc9f02)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>