We've seen issues where shell/python tasks lose their log file entries
or output and also where output is duplicated. Add some tests to attempt
to spot regressions in this area in future.
(From OE-Core rev: 414020a9bd656ee61efe2f47db1b31d86b15c1c8)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>