4.0 enhanche error message for connection failure (#353)

* Fixed comment about BoltConnectionError hiearchy

* Enhance error message for connection failure

Author: martin-neotech

neo4j/_exceptions.py

@@ -40,7 +40,13 @@ class BoltConnectionError(BoltError):
     """
 
     def __init__(self, message, address):
-        super().__init__(message, address)
+        msg = (
+        "Connection Failed. "
+        "Please ensure that your database is listening on the correct host and port and that you have enabled encryption if required. "
+        "Note that the default encryption setting has changed in Neo4j 4.0. See the docs for more information. "
+        "{}")
+
+        super().__init__(msg.format(message), address)
 
     def __str__(self):
         s = super().__str__()

neo4j/exceptions.py

@@ -55,8 +55,10 @@
   + BoltHandshakeError
   + BoltRoutingError
   + BoltConnectionError
+      + BoltSecurityError
+      + BoltConnectionBroken
+      + BoltConnectionClosed
   + BoltFailure
-  + BoltSecurityError
   + BoltIncompleteCommitError
   + BoltProtocolError
   + Bolt*