Drop 3.3, 3.4 and use single version docker images for all python tests (#7396)
* Create a new docker image for python 3.6
The previous one cannot build, because python3.6 was removed from
stretch.
* Drop support for 3.3 and 3.4
Also update all docker file to be single version
diff --git a/kokoro/linux/dockerfile/test/python37/Dockerfile b/kokoro/linux/dockerfile/test/python37/Dockerfile
new file mode 100644
index 0000000..c711eb8
--- /dev/null
+++ b/kokoro/linux/dockerfile/test/python37/Dockerfile
@@ -0,0 +1,23 @@
+FROM python:3.7-buster
+
+# Install dependencies. We start with the basic ones require to build protoc
+# and the C++ build
+RUN apt-get update && apt-get install -y \
+ autoconf \
+ autotools-dev \
+ build-essential \
+ bzip2 \
+ ccache \
+ curl \
+ gcc \
+ git \
+ libc6 \
+ libc6-dbg \
+ libc6-dev \
+ libgtest-dev \
+ libtool \
+ make \
+ parallel \
+ time \
+ wget \
+ && apt-get clean
