No module name for builtin type and exception names

Make utils.reflection.get_class_name() return just type name (without
module) for builtin exceptions and types. This makes output less
clumsy and makes this function return same strings for python 2 and 3.

Change-Id: Ibc599ed34c804cf2cf2ab67e7466a48ebe7f6df3
Python3 compatibility for utils.reflection

Refactor taskflow.utils.reflection to use six and py3-compatible
constructs.

Breaking change: drop class name from result of get_callable_name
for unbound methods. One can't get class name for unbound method
in python 3.

Change-Id: I98c5b33e7ee4520caf365aa87c9859ec967990de
Merge "No module name for builtin type and exception names"
Merge "Python3 compatibility for utils.reflection"