Drop python 3.5 support

Now that we released ussuri, we have a stable release that supports
3.5. That means if needed we can backport changes needed for
zuul and nodepool, so it should be safe to go ahead and drop 3.5
support.

Change-Id: Iaaba139009f2b49815c29717d71b9182a6bec2ab

.zuul.yaml

@@ -3,7 +3,6 @@
       - check-requirements
       - lib-forward-testing-python3
       - openstack-lower-constraints-jobs
-      - openstack-python35-jobs
       - openstack-python3-ussuri-jobs
       - openstacksdk-functional-tips
       - openstacksdk-tox-tips

py35-upper-constraints.txt

@@ -1,6 +0,0 @@
-oslo.i18n===3.25.1
-debtcollector===1.22.0
-oslotest===3.9.0
-reno===2.11.3
-oslo.config===7.0.0
-oslo.utils===3.42.1

releasenotes/notes/drop-python-3.5-362bb9d47f830353.yaml

@@ -0,0 +1,4 @@
+---
+upgrade:
+  - |
+    Python 3.5 is no longer supported.

setup.cfg

@@ -6,7 +6,7 @@ description-file =
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = https://docs.openstack.org/keystoneauth/latest/
-python-requires = >=3.5
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -17,7 +17,6 @@ classifier =
     Programming Language :: Python :: Implementation :: CPython
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8

tox.ini

@@ -18,12 +18,6 @@ whitelist_externals =
   bash
 basepython = python3
 
-[testenv:py35]
-deps =
-  -c{toxinidir}/py35-upper-constraints.txt
-  -r{toxinidir}/requirements.txt
-  -r{toxinidir}/test-requirements.txt
-
 [testenv:pep8]
 commands =
   flake8