oeqa/selftest/bblogging: Add logging tests for bb.build.exec_func with shell/python code

The situation regarding logging is different when a function called by
bb.build.exec_func() fails compared to when the task code fails
directly. There is a recent fix in bitbake to solve that and these
tests will hopefully prevent regressions.

Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>