System input plugin not implemented for Windows

[brianbaker]

Bug report

The System input plugin is not implemented for Windows.

Relevant telegraf.conf:

[[inputs.system]]

System info:

telegraf v1.2.1
windows server 2008r2

Steps to reproduce:

1. add [[inputs.system]] to telegraf.conf
2. see error in telegraf log: E! ERROR in input [inputs.system]: not implemented yet

Expected behavior:

The plugin would be implemented for Windows OR a disclaimer that it only works for unix-like systems.

Actual behavior:

No uptime data is logged.

Additional info:

As an alternative, win_perf_counters can be used to obtain the uptime:

[[inputs.win_perf_counters.object]]
  ObjectName = "System"
  Counters = [
    "System Up Time"
  ]
  Instances = ["------"]
  Measurement = "win_uptime"