Add python:3 action support.

Update tests to work in both Python 2 and Python 3.
Rename pythonaction to python3action for container image name for clarity.
Add tests for python:2 and python:3.
Add image names for all the actions. Rename javaaction to java8action for consistency.
diff --git a/settings.gradle b/settings.gradle
index ed84a46..1955feb 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -6,6 +6,7 @@
 include 'core:nodejs6Action'
 include 'core:actionProxy'
 include 'core:pythonAction'
+include 'core:python2Action'
 include 'core:swift3Action'
 include 'core:javaAction'
 
diff --git a/tests/build.gradle b/tests/build.gradle
index f9e95d9..32275c2 100644
--- a/tests/build.gradle
+++ b/tests/build.gradle
@@ -27,6 +27,7 @@
     ':core:nodejs6Action:distDocker',
     ':core:actionProxy:distDocker',
     ':core:pythonAction:distDocker',
+    ':core:python2Action:distDocker',
     ':core:javaAction:distDocker',
     ':core:swift3Action:distDocker',
     ':sdk:docker:distDocker',
diff --git a/tests/src/test/scala/actionContainers/ActionProxyContainerTests.scala b/tests/src/test/scala/actionContainers/ActionProxyContainerTests.scala
index 7c1e5a2..cee440b 100644
--- a/tests/src/test/scala/actionContainers/ActionProxyContainerTests.scala
+++ b/tests/src/test/scala/actionContainers/ActionProxyContainerTests.scala
@@ -56,9 +56,10 @@
 
         val python = """
                 |#!/usr/bin/env python
+                |from __future__ import print_function
                 |import sys
-                |print 'hello stdout'
-                |print >> sys.stderr, 'hello stderr'
+                |print('hello stdout')
+                |print('hello stderr', file=sys.stderr)
                 |print(sys.argv[1])
             """.stripMargin.trim
 
@@ -87,10 +88,10 @@
                 |#!/usr/bin/env python
                 |import os
                 |
-                |print '{ "api_host": "%s", "api_key": "%s", "namespace": "%s", "action_name" : "%s", "activation_id": "%s", "deadline": "%s" }' % (
+                |print('{ "api_host": "%s", "api_key": "%s", "namespace": "%s", "action_name" : "%s", "activation_id": "%s", "deadline": "%s" }' % (
                 |  os.environ['__OW_API_HOST'], os.environ['__OW_API_KEY'],
                 |  os.environ['__OW_NAMESPACE'], os.environ['__OW_ACTION_NAME'],
-                |  os.environ['__OW_ACTIVATION_ID'], os.environ['__OW_DEADLINE'])
+                |  os.environ['__OW_ACTIVATION_ID'], os.environ['__OW_DEADLINE']))
             """.stripMargin.trim
 
         val perl = """