Enable `flash-before` mode for devices connected via serial-pty
the same way, as for physical serial.
This mode allows Twister to start reading from the DUT's serial
connection only after the flashing stage has been completed,
thus excluding an early part of the log stream not directly
related to the current test.
It can help in situations, when the device is connected via some
serial-over-network harness which is still transferring device
logs or keeping in its buffer a tail with different RunID etc.
from the previous test image run.
Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>
Dmitrii Golovanov