Fix Issue with ClipperException and Docker not running case

clipper_admin/clipper_admin/docker/docker_container_manager.py

@@ -10,6 +10,7 @@
     CLIPPER_MGMT_FRONTEND_CONTAINER_LABEL, CLIPPER_INTERNAL_RPC_PORT,
     CLIPPER_INTERNAL_QUERY_PORT, CLIPPER_INTERNAL_MANAGEMENT_PORT)
 from ..exceptions import ClipperException
+from requests.exceptions import ConnectionError
 
 logger = logging.getLogger(__name__)
 
@@ -91,6 +92,10 @@ def start_clipper(self, query_frontend_image, mgmt_frontend_image,
         except docker.errors.APIError as e:
             logger.debug(
                 "{nw} network already exists".format(nw=self.docker_network))
+        except ConnectionError:
+            msg = "Unable to connect to Docker. Please Check if Docker is running."
+            raise ClipperException(msg)
+
 
         if not self.external_redis:
             logger.info("Starting managed Redis instance in Docker")

clipper_admin/clipper_admin/exceptions.py

@@ -1,7 +1,8 @@
 class ClipperException(Exception):
     """A generic exception indicating that Clipper encountered a problem."""
-
-    pass
+    def __init__(self, msg, *args):
+        self.msg = msg
+        super(Exception, self).__init__(msg, *args)
 
 
 class UnconnectedException(ClipperException):