Stop reactor even if post_update failed
Stop using Agent.quit() as signal handler

Use dedicated signal handler instead
Only log out if agent_id known, otherwise quit
Don't count stop attempts, instead use a timeout

Instead of  counting shutdown attempts, use a timeout to eventually shut
the agent down even if we could not logout from the master.
Command line option for shutdown timeout
Add missing period
Switch to utc time internally
Use http_retry_delay() instead of random()
Clarify help message for command line switch
Consistency in specifying argument type
Merge pull request #84 from guidow/rework_shutdown

Rework shutdown