If we see a BBHandledException in the idle handler, the understanding
is the system handled it, printing a log and traceback is just confusing.
Therefore only print these in the cases where its an unknown/unhandled
exception.
(Bitbake rev: d88ecc2bc44dce8fd92ca3a2c0fd4124a5e464fa)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>