twister: Don't print full stack trace in `readlines_until` method

The readlines_until method is part of the testing framework
(pytest harness) and should not print a full stack trace
when the expected line isn't found. It should also raise
an AssertionError instead of a TwisterHarnessTimeoutException,
allowing users to know that a test failed because the expected
condition did not happen.

Signed-off-by: Lukasz Fundakowski <lukasz.fundakowski@nordicsemi.no>
2 files changed