scripts: twisterlib: write full output of from pytest to twister harness

When pytest is executed, it only writes logging messages to the twister
harness, and does not include information about any test assertion
failures. This information is printed to stdout, so simply write
the contents stdout to the harness log.

Remove the log file arguments previously passed to pytest, as these are
no longer needed.

Signed-off-by: Daniel DeGrasse <ddegrasse@tenstorrent.com>