Rebuild python docker image (#5475)

* Rebuild python docker image

* Update docker image

* Change call to build_and_run_docker.sh

* Set up python tests for different versions

* Fix comments

kokoro/linux/python36_cpp/continuous.cfg

diff --git a/kokoro/linux/python36_cpp/continuous.cfg b/kokoro/linux/python36_cpp/continuous.cfg
new file mode 100644
index 0000000..b1b0e55
--- /dev/null
+++ b/kokoro/linux/python36_cpp/continuous.cfg
@@ -0,0 +1,11 @@
+# Config file for running tests in Kokoro
+
+# Location of the build script in repository
+build_file: "protobuf/kokoro/linux/python_cpp/build.sh"
+timeout_mins: 120
+
+action {
+  define_artifacts {
+    regex: "**/sponge_log.xml"
+  }
+}