jolokia: add 'server_' prefix to tags

it avoid overwriting the telegraf-wide host tag

plugins/inputs/jolokia/README.md

@@ -54,4 +54,4 @@ are collected for each server configured.
 See: https://jolokia.org/
 
 # Measurements:
-Jolokia plugin produces one measure for each metric configured, adding Server's `name`, `host` and `port` as tags.
+Jolokia plugin produces one measure for each metric configured, adding Server's `server_name`, `server_host` and `server_port` as tags.

plugins/inputs/jolokia/jolokia.go

@@ -222,9 +222,9 @@ func (j *Jolokia) Gather(acc telegraf.Accumulator) error {
 	tags := make(map[string]string)
 
 	for _, server := range servers {
-		tags["server"] = server.Name
-		tags["port"] = server.Port
-		tags["host"] = server.Host
+		tags["server_name"] = server.Name
+		tags["server_port"] = server.Port
+		tags["server_host"] = server.Host
 		fields := make(map[string]interface{})
 
 		for _, metric := range metrics {

plugins/inputs/jolokia/jolokia_test.go

@@ -96,9 +96,9 @@ func TestHttpJsonMultiValue(t *testing.T) {
 		"heap_memory_usage_used":      203288528.0,
 	}
 	tags := map[string]string{
-		"host":   "127.0.0.1",
-		"port":   "8080",
-		"server": "as1",
+		"server_host": "127.0.0.1",
+		"server_port": "8080",
+		"server_name": "as1",
 	}
 	acc.AssertContainsTaggedFields(t, "jolokia", fields, tags)
 }