Mutable types are used as default args

[jeffwidman]

I noticed there are a bunch of places where a mutable type is used for the default value. For example, there are a bunch of payloads=[] in kafka/client.py:

kafka-python/kafka/client.py

Line 591 in 3701690

def send_metadata_request(self, payloads=[], fail_on_error=True,

Using mutable types for default args is typically a no-no unless their surprising behavior is being explicitly abused, for an explanation see: http://effbot.org/zone/default-values.htm

I haven't spelunked in the code much, but I suspect:

1. They are an oversight rather than intentional.
2. A simple fix of switching these to tuples would solve the issue.