bump python versions and use docker slim versions (#1661)

Author: v1v

tests/Dockerfile

@@ -1,15 +1,20 @@
 ARG PYTHON_IMAGE
-FROM ${PYTHON_IMAGE}
+FROM ${PYTHON_IMAGE}-slim
 
 RUN apt-get -qq update && apt-get -qq -y --no-install-recommends install \
+    build-essential \
     ca-certificates \
     curl \
+    gnupg2 \
+    libmariadb-dev \
+    libpq-dev \
+    make \
     netcat \
     odbc-postgresql \
     unixodbc-dev \
     freetds-dev \
-    libmemcached-dev &&\
-    rm -rf /var/lib/apt/lists/*
+    libmemcached-dev \
+    && rm -rf /var/lib/apt/lists/*
 
 # connection to ha.pool.sks-keyservers.net fails sometimes, so let's retry with couple different servers
 RUN for server in $(shuf -e ha.pool.sks-keyservers.net \

tests/scripts/docker/black.sh

@@ -7,7 +7,7 @@ docker_pip_cache="/tmp/cache/pip"
 
 cd tests
 
-docker build --build-arg PYTHON_IMAGE=python:3.6 -t python-linters .
+docker build --build-arg PYTHON_IMAGE=python:3.8 -t python-linters .
 docker run \
   -e LOCAL_USER_ID=$UID \
   -e PIP_CACHE=${docker_pip_cache} \

tests/scripts/docker/flake8.sh

@@ -7,7 +7,7 @@ docker_pip_cache="/tmp/cache/pip"
 
 cd tests
 
-docker build --build-arg PYTHON_IMAGE=python:3.6 -t lint_flake8 .
+docker build --build-arg PYTHON_IMAGE=python:3.8 -t lint_flake8 .
 docker run \
   -e LOCAL_USER_ID=$UID \
   -e PIP_CACHE=${docker_pip_cache} \

tests/scripts/docker/isort.sh

@@ -7,7 +7,7 @@ docker_pip_cache="/tmp/cache/pip"
 
 cd tests
 
-docker build --build-arg PYTHON_IMAGE=python:3.6 -t python-linters .
+docker build --build-arg PYTHON_IMAGE=python:3.8 -t python-linters .
 docker run \
   -e LOCAL_USER_ID=$UID \
   -e PIP_CACHE=${docker_pip_cache} \