port source to python3

Signed-off-by: Ivana Hutarova Varekova <varekova@redhat.com>
fix some python3 problems find during testing

cupshelpers.py, PhysicalDevice.py, statereason.py use lt instead of cmp
asyncipp.py - use queue instead of Queue (and rename queue internal variable)
probe_printer.py, ... - use open instead of file
system-config-printer.py - use _thread stuff instead of thread one
__init__.py - fix import command

Signed-off-by: Ivana Hutarova Varekova <varekova@redhat.com>