Cleanup py27 support

This repo is now testing only with Python 3, so let's 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
- Update classifiers
- Remove install_command from tox.ini, the default is fine
- Use TOX_CONSTRAINTS_FILE instead of obsolete UPPER_CONSTRAINTS_FILE.

Change-Id: I4807e406cf6238767ceb02590c713f738686fa1f

setup.cfg

@@ -6,6 +6,7 @@ description-file =
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = https://docs.openstack.org/octavia-dashboard/latest/
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -13,6 +14,8 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     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
@@ -21,29 +24,3 @@ classifier =
 [files]
 packages =
     octavia_dashboard
-
-[build_sphinx]
-source-dir = doc/source
-build-dir = doc/build
-all_files = 1
-
-[upload_sphinx]
-upload-dir = doc/build/html
-
-[pbr]
-autodoc_tree_index_modules = False
-autodoc_tree_excludes =
-    setup.py
-    octavia_dashboard/tests
-    octavia_dashboard/enabled
-    octavia_dashboard/locale
-    octavia_dashboard/static
-    octavia_dashboard/conf
-    octavia_dashboard/local_settings.d
-    octavia_dashboard/post_install.sh
-    octavia_dashboard/karma.conf.js
-autodoc_index_modules = False
-autodoc_exclude_modules =
-    octavia_dashboard.tests.*
-    octavia_dashboard.enabled.*
-api_doc_dir = contributor/modules

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)

tox.ini

@@ -6,12 +6,11 @@ skipsdist = True
 [testenv]
 basepython = python3
 usedevelop = True
-install_command = pip install {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
    CLIENT_NAME=octavia-dashboard
    DJANGO_SETTINGS_MODULE=octavia_dashboard.tests.settings
-deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 whitelist_externals = npm
@@ -35,7 +34,7 @@ commands = npm install
 [testenv:docs]
 whitelist_externals = rm
 deps =
-    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+    -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/doc/requirements.txt
 commands =
@@ -54,10 +53,7 @@ commands =
 
 [testenv:releasenotes]
 whitelist_externals = rm
-deps =
+deps = {[testenv:docs]deps}
-    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
-    -r{toxinidir}/requirements.txt
-    -r{toxinidir}/doc/requirements.txt
 commands =
     rm -rf releasenotes/build
     sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html