Update python3 version info

In Train, we will use python 3.6 and 3.7 for python3 runtime
in our gate jobs [1]. This commit drops python 3.5 info
and adds python 3.6 and 3.7 info.

[1] https://governance.openstack.org/tc/reference/runtimes/train.html

Change-Id: I8f024505ed9b37c9f2b480f49b5000d75da42cc0

doc/source/contributor/testing.rst

@@ -103,11 +103,15 @@ py27dj18, py27dj19, py27dj110
 Runs the Python unit tests against Django 1.8, Django 1.9 and Django 1.10
 respectively
 
-
+py36
-py35
 ----
 
-Runs the Python unit tests with a Python 3.5 environment.
+Runs the Python unit tests with a Python 3.6 environment.
+
+py37
+----
+
+Runs the Python unit tests with a Python 3.7 environment.
 
 releasenotes
 ------------

doc/source/install/system-requirements.rst

@@ -2,13 +2,9 @@
 System Requirements
 ===================
 
-The Stein release of horizon has the following dependencies.
+The Train release of horizon has the following dependencies.
 
-* Python 2.7 or 3.5
+* Python 2.7, 3.6 or 3.7
-
-  * Python 3.6 support is experimental.
-  * Python 3.7 (or later versions if any) support will be considered
-    along with the OpenStack community support policy.
 
 * Django 1.11 or 2.0
 

setup.cfg

@@ -20,8 +20,8 @@ classifier =
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
     Topic :: Internet :: WWW/HTTP
 
 [global]