Paho Client Update

[xiazhvera]

Issue #, if available:

Description of changes:
Bring in paho client updates

paho v1.2

• Allow ^C to interrupt client loop.
• Fix for keepalive=0 causing an infinite disconnect/reconnect loop.
• Client.publish() now accepts bytes() payloads on Python 3.
• Don't attempt to join() own thread.
• Allow the use of Client.message_callback_add() from inside callbacks.

paho v1.3

• Handle unicode username and passwords correctly.

v1.4.0 - 2018-09-02

• Fix mid generation that was not thread-safe.
• Allow to remove authentication (reset username to None).
• Closes socket in client destructor to avoid FD leak.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.