Don't use */* in accept header

Pecan 1.4 uses accept header to decide the response content type.
Let's not use '*/*" in accept header as it returns text/plain in
case of errors.

fix: make README compatible with PyPI

Remove deprecated cli options

FIX Bug on workaround missing OS_AUTH_TYPE

os.environ.set doesn't existe, must use os.environ["OS_AUTH_TYPE"] = 
for setting environnement variable
https://docs.python.org/2/library/os.html

fix pep8

ignore W504[1]. tbh, not what i prefer.

[1] https://github.com/PyCQA/pycodestyle/issues/197

pep8: enable logging format checks

pep8: fix RST304 errors

Remove hacking dependency for pep8

Hacking is not maintained and depends on an old flake8 version.
Switch to flake8 and a few standard extensions.

tests: remove testtools and fixtures dependencies

Support Python 3.7 instead of 3.5

exeptions: fix matching when description is a dict

shell: fix OS_AUTH_TYPE workaround

Always use proxy method to get client

some methods were missing it, breaking respective openstackclient
commands.

Issue: #87

Update mergify configuration

Enable mergify

We recently uses local TZ, when timestamps doesn't have a TZ.
But Gnocchi client was passing the string as-is before allowing
all kind of timestamps that the server support (like +2hour, now, ...).

This change restores this feature.

This has a typo and is not actually useful. Remove it.

This patch remove usage of os_doc_tools.command and utilizes
cliff.sphinxext with minor modification.

The modification is required because original CommandManager
does not see gnocchi commands for some reason.

Fixes issue #80.

gnocchi status now returns 3 items. This change the tests
to ensure it works whatever the server side status return.