Add procstat lookup result information and always emit metric

plugins/inputs/procstat/README.md

@@ -136,18 +136,21 @@ implemented as a WMI query.  The pattern allows fuzzy matching using only
     - write_count (int, *telegraf* may need to be ran as **root**)
 - procstat_lookup
   - tags:
-    - exe (string)
-    - pid_finder (string)
-    - pid_file (string)
-    - pattern (string)
-    - prefix (string)
-    - user (string)
-    - systemd_unit (string)
-    - cgroup (string)
-    - win_service (string)
+    - exe
+    - pid_finder
+    - pid_file
+    - pattern
+    - prefix
+    - user
+    - systemd_unit
+    - cgroup
+    - win_service
+    - result
   - fields:
     - pid_count (int)
     - running (int)
+    - result_code (int, success = 0, lookup_error = 1)
+
 *NOTE: Resource limit > 2147483647 will be reported as 2147483647.*
 
 ### Example Output:

plugins/inputs/procstat/procstat.go

@@ -104,6 +104,14 @@ func (p *Procstat) Gather(acc telegraf.Accumulator) error {
 
 	pids, tags, err := p.findPids(acc)
 	if err != nil {
+		fields := map[string]interface{}{
+			"pid_count":   0,
+			"running":     0,
+			"result_code": 1,
+		}
+		tags["pid_finder"] = p.PidFinder
+		tags["result"] = "lookup_error"
+		acc.AddFields("procstat_lookup", fields, tags)
 		return err
 	}
 
@@ -119,10 +127,12 @@ func (p *Procstat) Gather(acc telegraf.Accumulator) error {
 	}
 
 	fields := map[string]interface{}{
-		"pid_count": len(pids),
-		"running":   len(procs),
+		"pid_count":   len(pids),
+		"running":     len(procs),
+		"result_code": 0,
 	}
 	tags["pid_finder"] = p.PidFinder
+	tags["result"] = "success"
 	acc.AddFields("procstat_lookup", fields, tags)
 
 	return nil