this block has a lot of code duplication.

Maybe we can do something like.
```
if options.key_comment:
    comment = 'having comment "%s"' % (options.key_comment)
else
    comment = ''

message = (
    'SSH key of type "%s" and length "%d" generated as '
    'public key file "%s" and private key file "%s"%s.') % (
    options.key_type,
    key_size,
    public_file,
    private_file,
    comment,
    )
```