Remove code still adjusting for Python 2
behavior based on version checks.

Change-Id: I29576a824278611d80991dce2501f14f1b262c76

Replace six with Python 3 style code.

Change-Id: I4b97e040f3e790ac114dcd43c68e6b67b1079adf

pycodestyle does not know about "importutils.try_import"
calls, so we have to either
  a) put them inside a "try" block
or
  b) add "# noqa: E402" to each import after the
     try_import call

Change-Id: Ia545bb689cfdfb57962d74e3957dfb372fd3782b

Importing pkg_resources has a side-effect of scanning all of the
installed python modules looking for entrypoints to build an in-memory
cache. Stevedore will be adding an on-disk cache to speed that process
up, which should provide significant performance benefits for client
applications such as python-openstackclient. This change introduces
stevedore to replace pkg_resources.

Change-Id: I66decf6d5a4f79ddaa6617737e9334a56dbbbad4
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

The __future__ module [1] was used in this context to ensure compatibility
between python 2 and python 3.

We previously dropped the support of python 2.7 [2] and now we only support
python 3 so we don't need to continue to use this module and the imports
listed below.

Imports commonly used and their related PEPs:
- `division` is related to PEP 238 [3]
- `print_function` is related to PEP 3105 [4]
- `unicode_literals` is related to PEP 3112 [5]
- `with_statement` is related to PEP 343 [6]
- `absolute_import` is related to PEP 328 [7]

[1] https://docs.python.org/3/library/__future__.html
[2] https://governance.openstack.org/tc/goals/selected/ussuri/drop-py27.html
[3] https://www.python.org/dev/peps/pep-0238
[4] https://www.python.org/dev/peps/pep-3105
[5] https://www.python.org/dev/peps/pep-3112
[6] https://www.python.org/dev/peps/pep-0343
[7] https://www.python.org/dev/peps/pep-0328

Change-Id: Id785793c36b3a6819a7522525252c3fef15ebe2b

IETF RFC 3986 classifies "~" as a reserved character [1],
however until python3.7 [2], python's url parsing
used to encode this character.

urllib has seen a lot of churn in various python
releases, and hence we were using a six wrapper
to shield ourselves, however, this backwards-incompatible
change in encoding norms forces us to deal with
the problem at our end.

Cinder's API accepts "~" in both, its encoded
or un-encoded forms. So, let's stop encoding it
within cinderclient, regardless of the version
of python running it.

Also fix an inconsitency around the use of the
generic helper method in utils added in
I3a3ae90cc6011d1aa0cc39db4329d9bc08801904
(cinderclient/utils.py - build_query_param)
to allow for False as a value in the query.

[1] https://tools.ietf.org/html/rfc3986.html
[2] https://docs.python.org/3/library/urllib.parse.html#url-quoting

Change-Id: I89809694ac3e4081ce83fd4f788f9355d6772f59
Closes-Bug: #1784728

We want to default to running all tox environments under python 3, so
set the basepython value in each environment.

We do not want to specify a minor version number, because we do not
want to have to update the file every time we upgrade python.

We do not want to set the override once in testenv, because that
breaks the more specific versions used in default environments like
py35 and py36.

Change-Id: I04b87b308a82113a57ea41bde0329e92b07b642e

This patch adds support for API microversion 3.16, which allows us to
pass --cluster optional argument to migration and manage operations.

For this, a new type of CLI argument is added, the mutually exclusive
arguments that can be used similarly to the utils.arg decorator, but
with utils.exclusive_arg decorator.

Implements: blueprint cinder-volume-active-active-support
Change-Id: If004715b9887d2a0f9fc630b44d6e11a4a8b778d