lshal: PipeRelay: use modern classes.

- Use android::base helpers
- Use std::thread instead of utils/Thread
- Use poll() instead of select()
- Use a separate fd trigger instead of an atomic_bool
  so that poll() finishes sooner.
- Also removes useless READ_TIMEOUT and error message
  for select() timeout and ~PipeRelay.

Test: lshal_test
Test: manually run lshal debug repeatedly to see if it
      is stuck or output is not complete

Bug: 182306776

Change-Id: Ie623bf1b979654a30b360819c9a787c88fd8d91d