twister: pytest: Log output passthrough

Pass Twister pytest plugin's log output, as well as output from
a test image running with pytest, up to Twister log irregardless
of the current verbosity level set at Twister.
This allows to collect full test output and also ensures that
recording data embedded in the test log is passed to the Twister
pytest harness for export.

Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>