Update internal block copy, total_done after last progress report (#762367)

Previously total_done was updated in copy_thread() after copying of the
blocks, but importantly before the last call to set_progress_info() to
update the progress bar.  Having total_done varying during the copy of a
single range of blocks, single call to copy_blocks::copy(), is an
impediment to being able to report a single progress bar across the
whole internal copy operation.

Move updating of total_done to copy() immediately after copy_thread()
completes.

Bug 762367 - Use a single progress bar for the whole of the internal
             copy operation