block-backend: Set werror/rerror defaults in blk_new()

Currently, the default values for werror and rerror have to be set
explicitly with blk_set_on_error() by the callers of blk_new(). The only
caller actually doing this is blockdev_init(), which is called for
BlockBackends created using -drive.

In particular, anonymous BlockBackends created with
-device ...,drive=<node-name> didn't get the correct default set and
instead defaulted to the integer value 0 (= BLOCKDEV_ON_ERROR_REPORT).
This is the intended default for rerror anyway, but the default for
werror should be BLOCKDEV_ON_ERROR_ENOSPC.

Set the defaults in blk_new() instead so that they apply no matter what
way the BlockBackend was created.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>

block/block-backend.c

@@ -325,6 +325,9 @@ BlockBackend *blk_new(uint64_t perm, uint64_t shared_perm)
     blk->shared_perm = shared_perm;
     blk_set_enable_write_cache(blk, true);
 
+    blk->on_read_error = BLOCKDEV_ON_ERROR_REPORT;
+    blk->on_write_error = BLOCKDEV_ON_ERROR_ENOSPC;
+
     block_acct_init(&blk->stats);
 
     notifier_list_init(&blk->remove_bs_notifiers);

tests/qemu-iotests/067.out

@@ -385,6 +385,7 @@ Testing: -device virtio-scsi -device scsi-cd,id=cd0
 {
     "return": [
         {
+            "io-status": "ok",
             "device": "",
             "locked": false,
             "removable": true,