Make the RPCVersionCapError message clearer

It is confusing to report that the version cap is too low, rather we
should report that the message version is too high.

Change-Id: Ic37eabb6f211fb68ca567ed4c400a1314e25cc68
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
Warns user if thread monkeypatch is not done

This change warns the user that it does have monkeypatched the
oslo.messaging library correclty.

Change-Id: Ice80ffc6cbc39919eac4bc0809992daea51b5922
Closes-bug: #1288878
Merge "Warns user if thread monkeypatch is not done"
Merge "Add functional and unit 0mq driver tests"
Merge "Make the RPCVersionCapError message clearer"