pkg/vminfo: remove Context from the constructor

[a-nogikh]

The context is assumed to be passed into the function doing the actual processing. Refactor vminfo to follow this approach.

This will help refactor pkg/rpcserver later.

[tarasmadan]

+1.
Just FYI: documentation: "Do not store Contexts inside a struct type; instead, pass a Context explicitly to each function that needs it. The Context should be the first parameter, typically named ctx"

[a-nogikh]

I tried to also remove the ctx Context field of the checkContext struct, but it was just too many little changes.