Fix #1148 - chatty MySQL

Two additional config options to reduce MySQL metrics

With:
 - gather_table_lock_waits = false
 - gather_event_waits = false

```
| wc -l
34
```

With:
 - gather_table_lock_waits = true
 - gather_event_waits = true

```
| wc -l
50040
```

closes #1148
closes #1149

etc/telegraf.conf

@@ -879,9 +879,15 @@
 #   ## gather metrics from PERFORMANCE_SCHEMA.TABLE_IO_WAITS_SUMMART_BY_TABLE
 #   gather_table_io_waits                     = false
 #   #
+#   ## gather metrics from PERFORMANCE_SCHEMA.TABLE_LOCK_WAITS
+#   gather_table_lock_waits                   = false
+#   #
 #   ## gather metrics from PERFORMANCE_SCHEMA.TABLE_IO_WAITS_SUMMART_BY_INDEX_USAGE
 #   gather_index_io_waits                     = false
 #   #
+#   ## gather metrics from PERFORMANCE_SCHEMA.EVENT_WAITS
+#   gather_event_waits                        = false
+#   #
 #   ## gather metrics from PERFORMANCE_SCHEMA.FILE_SUMMARY_BY_EVENT_NAME
 #   gather_file_events_stats                  = false
 #   #

plugins/inputs/mysql/README.md

@@ -56,9 +56,15 @@ This plugin gathers the statistic data from MySQL server
   ## gather metrics from PERFORMANCE_SCHEMA.TABLE_IO_WAITS_SUMMART_BY_TABLE
   gather_table_io_waits                     = false
   #
+  ## gather metrics from PERFORMANCE_SCHEMA.TABLE_LOCK_WAITS
+  gather_table_lock_waits                   = false
+  #
   ## gather metrics from PERFORMANCE_SCHEMA.TABLE_IO_WAITS_SUMMART_BY_INDEX_USAGE
   gather_index_io_waits                     = false
   #
+  ## gather metrics from PERFORMANCE_SCHEMA.EVENT_WAITS
+  gather_event_waits                        = false
+  #
   ## gather metrics from PERFORMANCE_SCHEMA.FILE_SUMMARY_BY_EVENT_NAME
   gather_file_events_stats                  = false
   #

plugins/inputs/mysql/mysql.go

@@ -25,7 +25,9 @@ type Mysql struct {
 	GatherSlaveStatus                   bool     `toml:"gather_slave_status"`
 	GatherBinaryLogs                    bool     `toml:"gather_binary_logs"`
 	GatherTableIOWaits                  bool     `toml:"gather_table_io_waits"`
+	GatherTableLockWaits                bool     `toml:"gather_table_lock_waits"`
 	GatherIndexIOWaits                  bool     `toml:"gather_index_io_waits"`
+	GatherEventWaits                    bool     `toml:"gather_event_waits"`
 	GatherTableSchema                   bool     `toml:"gather_table_schema"`
 	GatherFileEventsStats               bool     `toml:"gather_file_events_stats"`
 	GatherPerfEventsStatements          bool     `toml:"gather_perf_events_statements"`
@@ -68,9 +70,15 @@ var sampleConfig = `
   ## gather metrics from PERFORMANCE_SCHEMA.TABLE_IO_WAITS_SUMMART_BY_TABLE
   gather_table_io_waits                     = false
   #
+  ## gather metrics from PERFORMANCE_SCHEMA.TABLE_LOCK_WAITS
+  gather_table_lock_waits                   = false
+  #
   ## gather metrics from PERFORMANCE_SCHEMA.TABLE_IO_WAITS_SUMMART_BY_INDEX_USAGE
   gather_index_io_waits                     = false
   #
+  ## gather metrics from PERFORMANCE_SCHEMA.EVENT_WAITS
+  gather_event_waits                        = false
+  #
   ## gather metrics from PERFORMANCE_SCHEMA.FILE_SUMMARY_BY_EVENT_NAME
   gather_file_events_stats                  = false
   #
@@ -612,14 +620,18 @@ func (m *Mysql) gatherServer(serv string, acc telegraf.Accumulator) error {
 		}
 	}
 
-	err = m.gatherPerfTableLockWaits(db, serv, acc)
-	if err != nil {
-		return err
+	if m.GatherTableLockWaits {
+		err = m.gatherPerfTableLockWaits(db, serv, acc)
+		if err != nil {
+			return err
+		}
 	}
 
-	err = m.gatherPerfEventWaits(db, serv, acc)
-	if err != nil {
-		return err
+	if m.GatherEventWaits {
+		err = m.gatherPerfEventWaits(db, serv, acc)
+		if err != nil {
+			return err
+		}
 	}
 
 	if m.GatherFileEventsStats {