Update docker-py to current master (~docker-py 1.3.1)

The docker-py commit used in the standard `Dockerfile` is from Feb. 2015
and is out of date with the current API level and has fixes for things
like the new docker cli config location and registry v2 changes/API
responses as well.

Also pass "NOT_ON_HOST=true" to docker-py test suite so that tests
relying on direct HOST interaction (versus running in a container) are
skipped.

Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)

Dockerfile

@@ -131,7 +131,7 @@ RUN set -x \
 	&& rm -rf "$GOPATH"
 
 # Get the "docker-py" source so we can run their integration tests
-ENV DOCKER_PY_COMMIT 91985b239764fe54714fa0a93d52aa362357d251
+ENV DOCKER_PY_COMMIT 8a87001d09852058f08a807ab6e8491d57ca1e88
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \
 	&& git checkout -q $DOCKER_PY_COMMIT

hack/make/test-docker-py

@@ -12,7 +12,7 @@ set -e
 	}
 
 	# exporting PYTHONPATH to import "docker" from our local docker-py
-	test_env PYTHONPATH="$dockerPy" python "$dockerPy/tests/integration_test.py"
+	test_env PYTHONPATH="$dockerPy" NOT_ON_HOST=true python "$dockerPy/tests/integration_test.py"
 
 	bundle .integration-daemon-stop
 ) 2>&1 | tee -a "$DEST/test.log"