Check and store if we are a grandpa authority for sets.

[Zurcusa]

Currently, the nodeRole in HostConfig is a static field that stores the type of node we are starting. We need a way to distinguish if we're chosen for the current grandpa authority set as a voter. Alongside that, we need to store the key that we are selected to participate with so that we don't need to look it up in the keystone every time.