minor cleanup

- Reused contains() from utils.go at a couple of places
- Cleanup in return statements and boolean checks

cmd/xl-v1.go

@@ -95,13 +95,7 @@ func checkSufficientDisks(disks []string) error {
 
 // isDiskFound - validates if the disk is found in a list of input disks.
 func isDiskFound(disk string, disks []string) bool {
-	for _, d := range disks {
-		// Disk found return
-		if disk == d {
-			return true
-		}
-	}
-	return false
+	return contains(disks, disk)
 }
 
 // newXLObjects - initialize new xl object layer.