librbd: don't continue to remove an image w/ incompatible features

[yangdongsheng]

Fixes: http://tracker.ceph.com/issues/18315
Signed-off-by: Dongsheng Yang dongsheng.yang@easystack.cn

[yangdongsheng]

I don't think this is what Jason suggests as a fix for this issue. I had impression he wanted we check for incompatible features, while you just make it to abort when it fails to open the image.

@trociny IMO, the open operation will check the incompatible features, I want to reuse it. then abort the removal here. then it should be that:

if (r == -ENOSYS)
    return r;

But at the same time, I think we should only allow removal to continue when we got an -ENOENT in opening. So it turns out to be what it looks in this PR.

[dillaman]

lgtm -- solves issues like permission problems, incompatible features, etc.