add worker process name to w3wp processes

modify the `process` collector so that the IIS worker process name is
appended to the corresponding `w3wp` process.

before:
```
wmi_process_private_bytes{creating_process_id="2068",process="w3wp",process_id="12308"} 7.18204928e+08
```

after:
```
wmi_process_private_bytes{creating_process_id="2068",process="w3wp_our.website.com",process_id="12308"} 7.18204928e+08
```

reason:
We have some IIS servers hosting many .NET applications. When there is
resource contention on one of those servers, it's nice to know which IIS
application pool is the culprit.  Having only the process_id to
differentiate between w3wp processes requires additional work to figure
out which is which.  Also it does not allow for historial trending as
the process_id can change across restarts.

collector/process.go

@@ -177,6 +177,11 @@ type Win32_PerfRawData_PerfProc_Process struct {
 	WorkingSetPrivate       uint64
 }
 
+type WorkerProcess struct {
+	AppPoolName string
+	ProcessId   uint32
+}
+
 func (c *ProcessCollector) collect(ch chan<- prometheus.Metric) (*prometheus.Desc, error) {
 	var dst []Win32_PerfRawData_PerfProc_Process
 	q := queryAllWhere(&dst, c.queryWhereClause)
@@ -184,6 +189,10 @@ func (c *ProcessCollector) collect(ch chan<- prometheus.Metric) (*prometheus.Des
 		return nil, err
 	}
 
+	var dst_wp []WorkerProcess
+	q_wp := queryAll(&dst_wp)
+	wmi.QueryNamespace(q_wp, &dst_wp, "root\\WebAdministration")
+
 	for _, process := range dst {
 
 		if process.Name == "_Total" {
@@ -194,6 +203,13 @@ func (c *ProcessCollector) collect(ch chan<- prometheus.Metric) (*prometheus.Des
 		pid := strconv.FormatUint(uint64(process.IDProcess), 10)
 		cpid := strconv.FormatUint(uint64(process.CreatingProcessID), 10)
 
+		for _, wp := range dst_wp {
+			if wp.ProcessId == process.IDProcess {
+				processName = strings.Join([]string{processName, wp.AppPoolName}, "_")
+				break
+			}
+		}
+
 		ch <- prometheus.MustNewConstMetric(
 			c.StartTime,
 			prometheus.GaugeValue,