Major Logging Overhaul

in this commit:

- centralize logging output handler.
- set global Info/Debug/Error log levels based on config file or flags.
- remove per-plugin debug arg handling.
- add a I!, D!, or E! to every log message.
- add configuration option to specify where to send logs.

closes #1786

plugins/inputs/logparser/logparser.go

@@ -134,7 +134,7 @@ func (l *LogParserPlugin) Start(acc telegraf.Accumulator) error {
 	for _, filepath := range l.Files {
 		g, err := globpath.Compile(filepath)
 		if err != nil {
-			log.Printf("ERROR Glob %s failed to compile, %s", filepath, err)
+			log.Printf("E! Error Glob %s failed to compile, %s", filepath, err)
 			continue
 		}
 		files := g.Match()
@@ -167,7 +167,7 @@ func (l *LogParserPlugin) receiver(tailer *tail.Tail) {
 	var line *tail.Line
 	for line = range tailer.Lines {
 		if line.Err != nil {
-			log.Printf("ERROR tailing file %s, Error: %s\n",
+			log.Printf("E! Error tailing file %s, Error: %s\n",
 				tailer.Filename, line.Err)
 			continue
 		}
@@ -216,7 +216,7 @@ func (l *LogParserPlugin) Stop() {
 	for _, t := range l.tailers {
 		err := t.Stop()
 		if err != nil {
-			log.Printf("ERROR stopping tail on file %s\n", t.Filename)
+			log.Printf("E! Error stopping tail on file %s\n", t.Filename)
 		}
 		t.Cleanup()
 	}