Change aerospike plugin server tag to aerospike_host

This is to avoid a conflict with the standard "host" tag that is
used everywhere.

plugins/aerospike/aerospike.go

@@ -250,7 +250,7 @@ func get(key []byte, host string) (map[string]string, error) {
 func readAerospikeStats(stats map[string]string, acc plugins.Accumulator, host, namespace string) {
 	for key, value := range stats {
 		tags := map[string]string{
-			"host":      host,
+			"aerospike_host": host,
 			"namespace":      "_service",
 		}
 

plugins/aerospike/aerospike_test.go

@@ -67,7 +67,7 @@ func TestReadAerospikeStatsNamespace(t *testing.T) {
 	readAerospikeStats(stats, &acc, "host1", "test")
 
 	tags := map[string]string{
-		"host":      "host1",
+		"aerospike_host": "host1",
 		"namespace":      "test",
 	}
 	for k := range stats {