This solve a race condition where the client's thread poll triggers
connection(Lost|Failed) before a call to ask(). In that case a answer was
registered as expected and never cancelled, which lead to a frozen client.

- Split _connectToPrimaryNode
- Move ConnectionClosed at generic level

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2357 71dcc9de-d417-0410-9af5-da40c76e7ee4