Allow users to tell telegraf Agent not to include host tag

closes #848

agent/agent_test.go

@@ -1,7 +1,6 @@
 package agent
 
 import (
-	"github.com/stretchr/testify/assert"
 	"testing"
 	"time"
 
@@ -11,8 +10,18 @@ import (
 	_ "github.com/influxdata/telegraf/plugins/inputs/all"
 	// needing to load the outputs
 	_ "github.com/influxdata/telegraf/plugins/outputs/all"
+
+	"github.com/stretchr/testify/assert"
 )
 
+func TestAgent_OmitHostname(t *testing.T) {
+	c := config.NewConfig()
+	c.Agent.OmitHostname = true
+	_, err := NewAgent(c)
+	assert.NoError(t, err)
+	assert.NotContains(t, c.Tags, "host")
+}
+
 func TestAgent_LoadPlugin(t *testing.T) {
 	c := config.NewConfig()
 	c.InputFilters = []string{"mysql"}