Don't allow inputs to overwrite host tag

closes #1054

This affects tags in the following plugins:

- cassandra
- disque
- rethinkdb

plugins/inputs/cassandra/cassandra.go

@@ -9,17 +9,9 @@ import (
 	"io/ioutil"
 	"net/http"
 	"net/url"
-	//"reflect"
 	"strings"
 )
 
-/*type Server struct {
-	Host     string
-	Username string
-	Password string
-	Port     string
-}*/
-
 type JolokiaClient interface {
 	MakeRequest(req *http.Request) (*http.Response, error)
 }
@@ -55,12 +47,6 @@ type jmxMetric interface {
 	addTagsFields(out map[string]interface{})
 }
 
-func addServerTags(host string, tags map[string]string) {
-	if host != "" && host != "localhost" && host != "127.0.0.1" {
-		tags["host"] = host
-	}
-}
-
 func newJavaMetric(host string, metric string,
 	acc telegraf.Accumulator) *javaMetric {
 	return &javaMetric{host: host, metric: metric, acc: acc}
@@ -120,7 +106,7 @@ func (j javaMetric) addTagsFields(out map[string]interface{}) {
 
 	tokens := parseJmxMetricRequest(mbean)
 	addTokensToTags(tokens, tags)
-	addServerTags(j.host, tags)
+	tags["cassandra_host"] = j.host
 
 	if _, ok := tags["mname"]; !ok {
 		//Queries for a single value will not return a "name" tag in the response.
@@ -148,7 +134,7 @@ func addCassandraMetric(mbean string, c cassandraMetric,
 	fields := make(map[string]interface{})
 	tokens := parseJmxMetricRequest(mbean)
 	addTokensToTags(tokens, tags)
-	addServerTags(c.host, tags)
+	tags["cassandra_host"] = c.host
 	addValuesAsFields(values, fields, tags["mname"])
 	c.acc.AddFields(tokens["class"]+tokens["type"], fields, tags)
 
@@ -192,7 +178,7 @@ func (j *Cassandra) SampleConfig() string {
   servers = ["myuser:mypassword@10.10.10.1:8778","10.10.10.2:8778",":8778"]
   ## List of metrics collected on above servers
   ## Each metric consists of a jmx path.
-  ## This will collect all heap memory usage metrics from the jvm and 
+  ## This will collect all heap memory usage metrics from the jvm and
   ## ReadLatency metrics for all keyspaces and tables.
   ## "type=Table" in the query works with Cassandra3.0. Older versions might
   ## need to use "type=ColumnFamily"