Cleanup py27 support

Make a few cleanups:
- Remove python 2.7 stanza from setup.py
- Add requires on python >= 3.6 to setup.cfg so that pypi and pip
  know about the requirement
- Remove obsolete sections from setup.cfg:
  * Wheel is not needed for python 3 only repo
  * Some other sections are obsolete
- Update classifiers
- Update requirements, no need for python_version anymore
- Use sphinx-build

Change-Id: I8abd764d97a6711d3e6347ec3a7b8967f1512006

setup.cfg

@@ -7,6 +7,7 @@ author-email = openstack-discuss@lists.openstack.org
 home-page = https://docs.openstack.org/ironic-python-agent/
 summary = Ironic Python Agent Ramdisk
 license = Apache-2
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: System Administrators
@@ -14,9 +15,12 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: OS Independent
     Programming Language :: Python
+    Programming Language :: Python :: Implementation :: CPython
+    Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
+
 [files]
 packages =
     ironic_python_agent
@@ -55,16 +59,7 @@ ironic_python_agent.inspector.collectors =
 autodoc_index_modules = True
 api_doc_dir = contributor/api
 
-[build_sphinx]
-all_files = 1
-build-dir = doc/build
-source-dir = doc/source
-warning-is-error = 1
-
 [egg_info]
 tag_build =
 tag_date = 0
 tag_svn_revision = 0
-
-[wheel]
-universal = 1

setup.py

@@ -13,17 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# THIS FILE IS MANAGED BY THE GLOBAL REQUIREMENTS REPO - DO NOT EDIT
 import setuptools
 
-# In python < 2.7.4, a lazy loading of package `pbr` will break
-# setuptools if some other modules registered functions in `atexit`.
-# solution from: http://bugs.python.org/issue15881#msg170215
-try:
-    import multiprocessing  # noqa
-except ImportError:
-    pass
-
 setuptools.setup(
     setup_requires=['pbr>=2.0.0'],
     pbr=True)

test-requirements.txt

@@ -13,6 +13,6 @@ bandit!=1.6.0,>=1.1.0,<2.0.0 # Apache-2.0
 
 # Doc requirements
 doc8>=0.6.0 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4' # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD
 openstackdocstheme>=1.20.0 # Apache-2.0
 reno>=2.5.0 # Apache-2.0

tox.ini

@@ -64,7 +64,7 @@ commands = oslo_debug_helper -t ironic_python_agent/tests/unit {posargs}
 setenv = PYTHONHASHSEED=0
 sitepackages = False
 commands =
-  python setup.py build_sphinx
+  sphinx-build -b html doc/source doc/build/html
 
 [testenv:pdf-docs]
 whitelist_externals = make