Use c/storage/pkg/ioutils.AtomicWriteFiles to update auth.json

... so that users can't observe an intermediate empty, or partial, file.

(Note that there is still no locking, so two simultaneous updates to
auth.json might lose some updates.)

Fixes at least the worst impact of containers#1365 .

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

pkg/docker/config/config.go

@@ -15,6 +15,7 @@ import (
 	"github.com/containers/image/v5/pkg/sysregistriesv2"
 	"github.com/containers/image/v5/types"
 	"github.com/containers/storage/pkg/homedir"
+	"github.com/containers/storage/pkg/ioutils"
 	helperclient "github.com/docker/docker-credential-helpers/client"
 	"github.com/docker/docker-credential-helpers/credentials"
 	"github.com/hashicorp/go-multierror"
@@ -605,7 +606,7 @@ func modifyJSON(sys *types.SystemContext, editor func(auths *dockerConfigFile) (
 			return "", errors.Wrapf(err, "marshaling JSON %q", path)
 		}
 
-		if err = ioutil.WriteFile(path, newData, 0600); err != nil {
+		if err = ioutils.AtomicWriteFile(path, newData, 0600); err != nil {
 			return "", errors.Wrapf(err, "writing to file %q", path)
 		}
 	}