block: Stop passing flags to bdrv_reopen_queue_child()

block: Stop passing flags to bdrv_reopen_queue_child()

Now that all callers are passing the new options using the QDict we no
longer need the 'flags' parameter.

This patch makes the following changes:

   1) The update_options_from_flags() call is no longer necessary
      so it can be removed.

   2) The update_flags_from_options() call is now used in all cases,
      and is moved down a few lines so it happens after the options
      QDict contains the final set of values.

   3) The flags parameter is removed. Now the flags are initialized
      using the current value (for the top-level node) or the parent
      flags (after inherit_options()). In both cases the initial
      values are updated to reflect the new options in the QDict. This
      happens in bdrv_reopen_queue_child() (as explained above) and in
      bdrv_reopen_prepare().

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>