libpod/image: Use RepoDigests() in Inspect()

To get the more-robust handling from 0f6535c (libpod/image: Use
ParseNormalizedNamed in RepoDigests, 2019-01-08, containers#2106) here too.

Signed-off-by: W. Trevor King <wking@tremily.us>

libpod/image/image.go

@@ -824,9 +824,9 @@ func (i *Image) Inspect(ctx context.Context) (*inspect.ImageData, error) {
 		return nil, err
 	}
 
-	var repoDigests []string
-	for _, name := range i.Names() {
-		repoDigests = append(repoDigests, strings.SplitN(name, ":", 2)[0]+"@"+i.Digest().String())
+	repoDigests, err := i.RepoDigests()
+	if err != nil {
+		return nil, err
 	}
 
 	driver, err := i.DriverData()