selftests: tpm2: redirect python unittest logs to stdout

The python unittest module writes all its output to stderr, even when
the run is clean. Redirect its output logs to stdout.

Cc: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>