This library no longer supports Python 2, thus usage of six can be
removed. This also removes workaround about pickle library used in
Python 2 only.

Change-Id: I19d298cf0f402d65f0b142dea0bf35cf992332a9

python3.0 has deprecated LOG.warn
https://docs.python.org/3/library/logging.html#logging.warning
Closes-Bug: #1650843

Change-Id: Ib8473cbdb84547f385e619fe08ed723b1ee7bcdb

Also allows for people to create Atom's with a different rebind
or requires structure for the revert method, if desired.

Implements blueprint: seperate-revert-args

Change-Id: Ie7d13c8000ef08ff303481d486d1ba1cfbdeea44

* Moved common argument mapping logic to Atom
* Removed BaseTask
* Removed duplicated logic from subclasses

Change-Id: I275745adb80cecb0c35c1230eac76436bf3b0157

Instead of using the map() function (which depending
on the python version may return a list or an iterator
prefer to use the six.moves provided one and convert
that one to a list; this avoids creating extra lists
on versions of python where map() itself returns a
list).

This also adjusts some of the docstring to match the
style and format of other docstrings.

Change-Id: I29212016da95da6ca2bc6b3f103d03f7fcabf032

- Added a MapFunctorTask and ReduceFunctorTask to mimic the python
  builtin functions map and reduce, respectively

Change-Id: I29cd1249e1671aedfd2d25460d746b8d2154df2b

Prefer the non-deprecated 'oslo_utils' instead of
the namespaced 'oslo.utils' wherever it was previously
used.

Change-Id: I9a78150ef5266e1ff22147278162fe3cfe1b2e3f

The reflection module is now part of oslo.utils so we should
remove our local version and use that version instead; this
also goes for the uuidutils module which is now part of
oslo.utils as well so we no longer need our local version
copied from the incubator...

Note that one reflection method `find_subclasses` which was to
specific to taskflow is now moved to the misc utility module
instead of its prior home in the reflection module.

Change-Id: I069881c80b0b2916cc0c414992b80171f7eeb79f

Instead of having code that is some what like the notifier
code we already have, but is duplicated and is slightly different
in the task class just move the code that was in the task class (and
doing similar actions) to instead now use a notifier that is directly
contained in the task base class for internal task triggering of
internal task events.

Breaking change: alters the capabilities of the task to process
notifications itself, most actions now must go through the task
notifier property and instead use that (update_progress still exists
as a common utility method, since it's likely the most common type
of notification that will be used).

Removes the following methods from task base class (as they are
no longer needed with a notifier attribute):

- trigger (replaced with notifier.notify)
- autobind (removed, not replaced, can be created by the user
            of taskflow in a simple manner, without requiring
            functionality in taskflow)
- bind (replaced with notifier.register)
- unbind (replaced with notifier.unregister)
- listeners_iter (replaced with notifier.listeners_iter)

Due to this change we can now also correctly proxy back events from
remote tasks to the engine for correct proxying back to the original
task.

Fixes bug 1370766

Change-Id: Ic9dfef516d72e6e32e71dda30a1cb3522c9e0be6

Add a misc.clamp function that will clamp a value to a given
range (it can also call a callback if clamping occurs). Use it
to clamp the progress value that was previously clamped with
a set of customized logic that can now be replaced with a more
generalized logic that can be shared.

Change-Id: I8369dbb61f73a60932d9e15c8b4d06db249ea38e