push: fix push with one argument

When doing a `podman push $IMG`, $IMG acts as the source and the
destination.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

cmd/podman/images/push.go

@@ -98,6 +98,7 @@ func imagePush(cmd *cobra.Command, args []string) error {
 	switch len(args) {
 	case 1:
 		source = args[0]
+		destination = args[0]
 	case 2:
 		source = args[0]
 		destination = args[1]