test: fix spec issues to meet paho test runs

Fix paho failing tests (#174)

fix: SignalDisconnect before SignalOffline
Handles case when Disconnect from client provides SessionExpiryInterval

fix: tag name for RetainAvailable parameter
fix: send the username to ACL on publish
refactor: check for topic alias when the packet arrived
  prevent double-checking for ACL
refactor: decrement children count on node delete
refactor: set publish stub before unsubscribing
fix: fix to #173
  Shutdown subscriber when the session expire fired.
  Prevents subscriber from leaking.
refactor: incoming PUBLISH messages
  handle flow control as per spec

fix: return of granted QoS
refactor: send disconnect from connection close stage 2 only
refactor: clone PUBLISH packet before sending from a topic manager