Graphite TCP should not block system shutdown

[otoolep]

With this change Graphite TCP connections are tracked on a per-service
basis. This allows a closing Graphite service to first shutdown any
active connections, thereby unblocking the rest of shutdowm.

This work exposed small shortcomings with the existing Diagnostics
system and that code has alse been tweaked.

Fixes issue #4017

[otoolep]

Diagnostics now on a per-Service basis:

name: graphite:tcp::2004
------------------------
local           remote          connect time
127.0.0.1:2004  127.0.0.1:39541 2015-09-24T20:45:09.677914798Z

name: graphite:tcp::2003
------------------------
local           remote          connect time
127.0.0.1:2003  127.0.0.1:44387 2015-09-24T20:45:10.386430546Z

[otoolep]

@dgnorton

[dgnorton]

+1