We found some SD card on Raspberry Pi could have very bad performance.
It could take seconds to save small amount of data.
If the DUT receives data and save it as log, then it stops receiving data until log is saved.
This could lead to expect timeout. As an workaround to this issue,
``BaseDUT`` class will create a thread to save logs.
Then data will be passed to ``expect`` as soon as received.
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