Add functional and unit 0mq driver tests

Basic functional and unit tests for zmq driver.

Note as the zmq driver is directly dependent on eventlet, this
change also updates the notify logger tests to remove the
direct dependency on threading which was being monkey patched,
causing test failures.

As the zmq driver has a direct dependency on eventlet, tests are
skipped under py3.

Co-Authored-By: Kapil Thangavelu <kapil.thangavelu@canonical.com>
Co-Authored-By: Edward Hope-Morley <edward.hope-morley@canonical.com>

Change-Id: I93b8b2e92d0f2a353d3357a5e61f6d472ec84944
Partial-bug: #1302941
Merge "Add functional and unit 0mq driver tests"