Resolved use of -o option, was failing with new pyzmq

Checks for setsockopt availability was using fixed zmq.core.constants, which
has changed to zmq.sugar in later versions.

Modified as before for socket types and shall work with both new and older
pyzmq.

Test case for using -o option on PUB added.
        modified:   lib/zmqc.py
        modified:   tests/test_it.py
Enhanced testing, added binding to random port

        modified:   tests/conftest.py
        modified:   tests/test_it.py
        modified:   tox.ini
Deleted obsolete lines (were already commented out)

        modified:   tests/conftest.py