For every peer expose through `getpeerinfo` RPC whether or not we selected them as HB peers, and whether or not they selected us as HB peers.

Suggestion by @gmaxwell.
{
    while (!flagInterruptMsgProc)
    {
        std::vector<CNode*> vNodesCopy;
        {
            LOCK(cs_vNodes);
            vNodesCopy = vNodes;
            for (CNode* pnode : vNodesCopy) {
                pnode->AddRef();
            }
        }
        bool fMoreWork = false;