func (s *JSONStore) Stop(ctx context.Context, wait bool) error {
	if wait {
		s.WG.Wait()
	}
	return s.WriteState(ctx)
}
Stop writes out the state if requested by StateInputFilename.

This function first waits for s.WG if told to.
package sio
import (
	"context"
	"encoding/json"
	"io/ioutil"
	"sync"
	"github.com/Comcast/sheens/crew"
)
type JSONStore struct {
	StateOutputFilename string
	StateInputFilename string
	state map[string]*crew.Machine
	WG sync.WaitGroup
}
func NewJSONStore() *JSONStore {
	return &JSONStore{}
}
func (s *JSONStore) Start(ctx context.Context) error {
	return nil
}