api switch support

[outscale-mgo]

osc-cli need an api selection before making any call.

examples osc-cli api ReadVms here have api
oapi-cli remove the arguments, problem, we might at some points have more than one api (like fcu, lbu and so on)

it could be require like in osc-cli, but it doesn't make sense, as peoples make api separator like they make namespaces in OOP, thinking there will be name collision, but in reality, name collision never happen.

I mean sure at some points it might happen, but look at linux code source that is 20+M lines of code and still manage to avoid them with a language that doesn't support namespace.

And most Outscale calls are like ReadVms, ReadVolumes, if the api name was Volumes/Vms. then osc-cli vms read would make sense, but it's not.

Therefore we can safely assume that 99.9% of the time api specification will be useless, and be require only for peoples who think that name collision will happen, but, if we don't have it, peoples will be scare than something that never happen, will happen.