logictest: improve progress output

Logictests would print some progress messages to stdout as they run.
Each file prints when it ends and, while it's running, it prints
messages when statements finish successfully (but only up to once per
2s). This patch adds a second-level timestamp to those messages, in
order to provide more clues in the output of timed out logictest
packages. Otherwise, I'm always left guessing if the package had been
making constant progress until the timeout, or if it got stuck at some
point.

Release note: None

pkg/sql/logictest/logic.go

@@ -1280,7 +1280,10 @@ func (t *logicTest) close() {
 // verbose is set.
 func (t *logicTest) outf(format string, args ...interface{}) {
 	if t.verbose {
-		fmt.Printf(format, args...)
+		finalArgs := make([]interface{}, 1+len(args))
+		finalArgs[0] = time.Now().Format("15:04:05")
+		copy(finalArgs[1:], args)
+		fmt.Printf("[%s] "+format, finalArgs...)
 		fmt.Println()
 		log.Infof(context.Background(), format, args...)
 	}