Pull request: querylog bug fix

Merge in DNS/adguard-home from 2324-querylog-bug-fix to master

Closes #2324.

Squashed commit of the following:

commit fdd584a218e1edc3e45ab5b00ceed0a3be681e32
Merge: 8103f9e42 f2eda6d19
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Wed Nov 18 15:35:42 2020 +0300

    Merge branch 'master' into 2324-querylog-bug-fix

commit 8103f9e42a398f43682ee30d09b3afdab0e9e177
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Wed Nov 18 14:28:29 2020 +0300

    querylog: fix the file ordering bug

commit 2c4e8fcc5b8593be1614480508dfd600fc676e64
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Nov 17 20:57:45 2020 +0300

    querylog: wrap errors to clarify error trace

commit 3733062b494817696e4443f153774bb01cea1b06
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Nov 17 18:55:17 2020 +0300

    querylog: fix logger output bug

internal/agherr/agherr_test.go

@@ -48,7 +48,7 @@ func TestError_Unwrap(t *testing.T) {
 	)
 	errs := []error{
 		errSimple:  errors.New("a"),
-		errWrapped: fmt.Errorf("%w", errors.New("nested")),
+		errWrapped: fmt.Errorf("err: %w", errors.New("nested")),
 		errNil:     nil,
 	}
 	testCases := []struct {