block: check return value of bdrv_open_child and drop error propagation

block: check return value of bdrv_open_child and drop error propagation

This patch is generated by cocci script:

@@
symbol bdrv_open_child, errp, local_err;
expression file;
@@

  file = bdrv_open_child(...,
-                        &local_err
+                        errp
                        );
- if (local_err)
+ if (!file)
  {
      ...
-     error_propagate(errp, local_err);
      ...
  }

with command

spatch --sp-file x.cocci --macro-file scripts/cocci-macro-file.h \
--in-place --no-show-diff --max-width 80 --use-gitgrep block

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20210202124956.63146-4-vsementsov@virtuozzo.com>
[eblake: fix qcow2_do_open() to use ERRP_GUARD, necessary as the only
caller to pass allow_none=true]
Signed-off-by: Eric Blake <eblake@redhat.com>