Update Jenkinsfile to perform existing jenkins tasks

Signed-off-by: Mike Dougherty <mike.dougherty@docker.com>

script/test/all

@@ -24,6 +24,7 @@ fi
 
 
 BUILD_NUMBER=${BUILD_NUMBER-$USER}
+PY_TEST_VERSIONS=${PY_TEST_VERSIONS:-py27,py34}
 
 for version in $DOCKER_VERSIONS; do
   >&2 echo "Running tests against Docker $version"
@@ -58,6 +59,6 @@ for version in $DOCKER_VERSIONS; do
     --env="DOCKER_VERSION=$version" \
     --entrypoint="tox" \
     "$TAG" \
-    -e py27,py34 -- "$@"
+    -e "$PY_TEST_VERSIONS" -- "$@"
 
 done