build: update logging statements to make json log work - fixes #6038

This changes log statements from log to fs package, which is required for --use-json-log
to properly make log output in JSON format. The recently added custom linting rule,
handled by ruleguard via gocritic via golangci-lint, warns about these and suggests
the alternative. Fixing was therefore basically running "golangci-lint run --fix",
although some manual fixup of mainly imports are necessary following that.

vfs/test_vfs/test_vfs.go

@@ -7,7 +7,6 @@ import (
 	"flag"
 	"fmt"
 	"io"
-	"log"
 	"math"
 	"math/rand"
 	"os"
@@ -16,6 +15,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/lib/file"
 	"github.com/rclone/rclone/lib/random"
 )
@@ -93,13 +93,13 @@ func (t *Test) randomTest() {
 // logf logs things - not shown unless -v
 func (t *Test) logf(format string, a ...interface{}) {
 	if *verbose {
-		log.Printf(t.prefix+format, a...)
+		fs.Logf(nil, t.prefix+format, a)
 	}
 }
 
 // errorf logs errors
 func (t *Test) errorf(format string, a ...interface{}) {
-	log.Printf(t.prefix+"ERROR: "+format, a...)
+	fs.Logf(nil, t.prefix+"ERROR: "+format, a)
 }
 
 // list test
@@ -286,7 +286,7 @@ func main() {
 	flag.Parse()
 	args := flag.Args()
 	if len(args) != 1 {
-		log.Fatalf("%s: Syntax [opts] <directory>", os.Args[0])
+		fs.Fatalf(nil, "%s: Syntax [opts] <directory>", os.Args[0])
 	}
 	dir := args[0]
 	_ = file.MkdirAll(dir, 0777)