block/backup: centralize copy_bitmap initialization

Just a few housekeeping changes that keeps the following commit easier
to read; perform the initial copy_bitmap initialization in one place.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190716000117.25219-8-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
1 file changed