brick-mux : fix error handling

Fix error handling from ReadFromPidFile call. Also added a check to
bypass detach if the brick pid is -1.

Signed-off-by: Atin Mukherjee <amukherj@redhat.com>

Author: Atin Mukherjee

glusterd2/brickmux/demultiplex.go

@@ -32,11 +32,17 @@ func Demultiplex(b brick.Brickinfo) error {
 	if err != nil {
 		return err
 	}
-	if pidOnFile, err = daemon.ReadPidFromFile(brickDaemon.PidFile()); err == nil {
+	if pidOnFile, err = daemon.ReadPidFromFile(brickDaemon.PidFile()); err != nil {
 		log.WithFields(log.Fields{"brick": b.String(),
 			"pidfile": brickDaemon.PidFile()}).Error("Failed to read the pidfile")
 		return err
 
+	}
+	if pidOnFile == -1 {
+		log.WithFields(log.Fields{"brick": b.String(),
+			"pidfile": brickDaemon.PidFile()}).Error("Pid is -1")
+		return err
+
 	}
 	brickDaemon.Socketfilepath, err = glusterdGetSockFromBrickPid(pidOnFile)
 	if err != nil {