Update wmi_windows.go

fixes compile error on windows because of changed collect.Add() method signature, now requiring a opentsb.TagSet as second parameter and the value as third parameter
Update wmi_windows.go
Merge pull request #15 from wech71/patch-1

Update wmi_windows.go
Error on bad winsvc command
Restrict cassandra and hbase to linux and darwin
Stop logging on each batch sent
Init collect hostname correctly

Since Add and Set can now be called during init(), hostname should be set
during check instead of Init.
Use our standard init check method pattern for iis and sql

This prevents the log from getting spammed with exceptions every 15s.

The SQL collectors are also merged into one because it's simpler and they
didn't need to be separate.
Simpler service loop
Remove unused service args
Kill WMI on service stop
Don't run any service code if we're in WMI mode
Merge branch 'master' of https://github.com/StackExchange/scollector into StackExchange-master

Conflicts:
	collectors/wmi_windows.go
Merge branch 'StackExchange-master'