gapi: Add world interface and refactor existing code to use it

This is the initial base of what will hopefully become a powerful API
that machines will use to communicate. It will be the basis of the
stateful data store that can be used for exported resources, fact
exchange, state machine flags, locks, and much more.

gapi/gapi.go

@@ -19,14 +19,23 @@
 package gapi
 
 import (
-	"github.com/purpleidea/mgmt/etcd"
 	"github.com/purpleidea/mgmt/pgraph"
+	"github.com/purpleidea/mgmt/resources"
 )
 
+// World is an interface to the rest of the different graph state. It allows
+// the GAPI to store state and exchange information throughout the cluster. It
+// is the interface each machine uses to communicate with the rest of the world.
+type World interface { // TODO: is there a better name for this interface?
+	ResExport([]resources.Res) error
+	// FIXME: should this method take a "filter" data struct instead of many args?
+	ResCollect(hostnameFilter, kindFilter []string) ([]resources.Res, error)
+}
+
 // Data is the set of input values passed into the GAPI structs via Init.
 type Data struct {
 	Hostname string // uuid for the host, required for GAPI
-	EmbdEtcd *etcd.EmbdEtcd
+	World    World
 	Noop     bool
 	NoWatch  bool
 	// NOTE: we can add more fields here if needed by GAPI endpoints