copy: progress bar: show messages on completion
copy: progress bar: show messages on completion

Show messages on completion of the progress bars:
```
Copying blob 6292a0d81fc0 done
```
...when the copy operation is completed.

```
Copying blob 6292a0d81fc0 done: already exists
```
...when the blob already exists in the local storage.

As we cannot update progress bars on the fly, we need to defer their
creation to the point we know if a copy operations must be executed
or nor (i.e., to copyLayer()).

Signed-off-by: Valentin Rothberg <c8d7c67387706f1534261b1aba83f5c355c00ff5@redhat.com>

containers/image,containers/image