qemu-img: Fix qemu-img convert -n

If -n is specified, it does not matter whether the output format and
protocol support image creation; building the creation options should
simply be skipped.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-id: 1423666727-20777-2-git-send-email-mreitz@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

qemu-img.c

@@ -1531,6 +1531,7 @@ static int img_convert(int argc, char **argv)
         goto out;
     }
 
+    if (!skip_create) {
         if (!drv->create_opts) {
             error_report("Format driver '%s' does not support image creation",
                          drv->format_name);
@@ -1560,6 +1561,7 @@ static int img_convert(int argc, char **argv)
         if (ret < 0) {
             goto out;
         }
+    }
 
     /* Get backing file name if -o backing_file was used */
     out_baseimg_param = qemu_opt_get(opts, BLOCK_OPT_BACKING_FILE);