Change “node_info” RPC to accept multiple VGs/hypervisors

Keeping the node state up to date will require information from multiple
VGs and hypervisors. Instead of requiring multiple calls this change
allows a single call to return all needed information. Existing users
are changed.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>