selftests: ublk: increase timeouts for parallel test execution

selftests: ublk: increase timeouts for parallel test execution

When running tests in parallel with high JOBS count (e.g., JOBS=64),
the existing timeouts can be insufficient due to system load:

- Increase state wait loops from 20/50 to 100 iterations in
  _recover_ublk_dev(), __ublk_quiesce_dev(), and __ublk_kill_daemon()
  to handle slower state transitions under heavy load

- Add --timeout=20 to udevadm settle calls to prevent indefinite
  hangs when udev event queue is overwhelmed by rapid device
  creation/deletion

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>