FFE for python-taskflow 0.7.1

* Needed for OpenStack kilo rc1.
* All reverse-depends are OpenStack components.
* Tested alongside Kilo RC1 in PPA

0.7.1
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* Revert "Add retries to fetching the zookeeper server version"
* Allow turning off the version check
* adding check for str/unicode type in requires
* Add retries to fetching the zookeeper server version
* Remove duplicate 'the' and link to worker engine section
* Remove delayed decorator and replace with nicer method
* Fix log statement
* Make the atom class an abstract class
* Mark conductor 'stop' method deprecation kwarg with versions
* Move to hacking 0.10
* catch NotFound errors when consuming or abandoning
* Use the new table length constants
* Improve upon/adjust/move around new optional example
* Clarify documentation related to inputs
* Docstrings should document parameters return values
* Let the multi-lock convert the provided value to a tuple
* Map optional arguments as well as required arguments
* Add a BFS tree iterator
* DFS in right order when not starting at the provided node
* Rework the sqlalchemy backend
* Modify stop and add wait on conductor to prevent lockups
* Default to using a thread-safe storage unit
* Add warning to sqlalchemy backend size limit docs
* Updated from global requirements
* Use a thread-identifier that can't easily be recycled
* Use a notifier instead of a direct property assignment
* Tweak the WBE diagram (and present it as an svg)
* Remove duplicate code
* Improved diagram for Taskflow
* Bump up the env_builder.sh to 2.7.9
* Add a capturing listener (for test or other usage)
* Add + use a staticmethod to fetch the immediate callables
* Just directly access the callback attributes
* Use class constants during pformatting a tree node