Update docker-py

This fix update docker-py so that containers from the tests run
could be cleaned up during teardown:
```diff
-ENV DOCKER_PY_COMMIT 5e28dcaace5f7b70cbe44c313b7a3b288fa38916
+ENV DOCKER_PY_COMMIT 8b246db271a85d6541dc458838627e89c683e42f
```

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
(cherry picked from commit 66935a0f64f0a72162fb3919c759f4f500b6c372)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

components/engine/Dockerfile

@@ -142,7 +142,7 @@ RUN set -x \
 	&& rm -rf "$GOPATH"
 
 # Get the "docker-py" source so we can run their integration tests
-ENV DOCKER_PY_COMMIT 5e28dcaace5f7b70cbe44c313b7a3b288fa38916
+ENV DOCKER_PY_COMMIT 8b246db271a85d6541dc458838627e89c683e42f
 # To run integration tests docker-pycreds is required.
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \

components/engine/Dockerfile.aarch64

@@ -106,7 +106,7 @@ RUN set -x \
 	&& rm -rf "$GOPATH"
 
 # Get the "docker-py" source so we can run their integration tests
-ENV DOCKER_PY_COMMIT 5e28dcaace5f7b70cbe44c313b7a3b288fa38916
+ENV DOCKER_PY_COMMIT 8b246db271a85d6541dc458838627e89c683e42f
 # To run integration tests docker-pycreds is required.
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \

components/engine/Dockerfile.armhf

@@ -104,7 +104,7 @@ RUN set -x \
 	&& rm -rf "$GOPATH"
 
 # Get the "docker-py" source so we can run their integration tests
-ENV DOCKER_PY_COMMIT 5e28dcaace5f7b70cbe44c313b7a3b288fa38916
+ENV DOCKER_PY_COMMIT 8b246db271a85d6541dc458838627e89c683e42f
 # To run integration tests docker-pycreds is required.
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \

components/engine/Dockerfile.ppc64le

@@ -102,7 +102,7 @@ RUN set -x \
 	&& rm -rf "$GOPATH"
 
 # Get the "docker-py" source so we can run their integration tests
-ENV DOCKER_PY_COMMIT 5e28dcaace5f7b70cbe44c313b7a3b288fa38916
+ENV DOCKER_PY_COMMIT 8b246db271a85d6541dc458838627e89c683e42f
 # To run integration tests docker-pycreds is required.
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \

components/engine/Dockerfile.s390x

@@ -96,7 +96,7 @@ RUN set -x \
 	&& rm -rf "$GOPATH"
 
 # Get the "docker-py" source so we can run their integration tests
-ENV DOCKER_PY_COMMIT 5e28dcaace5f7b70cbe44c313b7a3b288fa38916
+ENV DOCKER_PY_COMMIT 8b246db271a85d6541dc458838627e89c683e42f
 # To run integration tests docker-pycreds is required.
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \