If a python function exec_func() calls a shell task, the logging wasn't working
correctly in all cases since the exception was turned into a BBHandledException()
and the logfile piece was lost which is handled at the top task level.
The easiest way to avoid this is to allow the ExecutionError exceptions to
be raised to a higher level, we don't need the traceback for them.
(Bitbake rev: 7cae11f558f9ff5fd05ef23b789aaef92fb5a327)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>