objcore/req symmetry and Obj->methods

[Dridi Boukelmoune]

> Comments, inputs, thoughts ?

I don't have a deep knowledge of the stevedore API, so I'll share my
cents on the side topic instead...

> [1] Actually, it's not obvious to me that we should have the "magic"
>     path for synthetic any more, why don't we just push a synthetic
>     backend and use the regular path ?

Could you please elaborate on pushing a synthetic backend? Would it be
a kind of one-off backend like the cgi example we discussed earlier?

It sounds good, but there may be issues like seeing an actual bereq in
the log. It may lead to confusing user experience, I need more time to
think about it.