ZioCtrl: implement __str__ like zio-dump

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
ZioCharDevice: add poll() support

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
ZioInterface.py: use poll to check if device is ready for I/O

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
PyZio: fix package export

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
PyZio: add logging prints

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
PyZio: export ZioUtils functions

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>