Fix err race condition and partial failure issues

closes #1439
closes #1440
closes #1441
closes #1442
closes #1443
closes #1444
closes #1445

plugins/inputs/mongodb/mongodb.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal/errchan"
 	"github.com/influxdata/telegraf/plugins/inputs"
 	"gopkg.in/mgo.v2"
 )
@@ -55,9 +56,7 @@ func (m *MongoDB) Gather(acc telegraf.Accumulator) error {
 	}
 
 	var wg sync.WaitGroup
-
-	var outerr error
-
+	errChan := errchan.New(len(m.Servers))
 	for _, serv := range m.Servers {
 		u, err := url.Parse(serv)
 		if err != nil {
@@ -73,13 +72,12 @@ func (m *MongoDB) Gather(acc telegraf.Accumulator) error {
 		wg.Add(1)
 		go func(srv *Server) {
 			defer wg.Done()
-			outerr = m.gatherServer(srv, acc)
+			errChan.C <- m.gatherServer(srv, acc)
 		}(m.getMongoServer(u))
 	}
 
 	wg.Wait()
-
-	return outerr
+	return errChan.Error()
 }
 
 func (m *MongoDB) getMongoServer(url *url.URL) *Server {