Move the common part of IDE/SCSI/virtio error handling to the block
layer.  The new function bdrv_error_action subsumes all three of
bdrv_emit_qmp_error_event, vm_stop, bdrv_iostatus_set_err.

The same scheme will be used for errors in block jobs.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>