lib, gapi: Next method of GAPI should generate first event

This puts the generation of the initial event into the Next method of
the GAPI. If it does not happen, then we will never get a graph. This is
important because this notifies the GAPI when we're actually ready to
try and generate a graph, rather than blocking on the Graph method if we
have a long compile for example.

This is also required for the etcd watch cleanup.

puppet/gapi.go

@@ -76,9 +76,6 @@ func (obj *GAPI) Graph() (*pgraph.Graph, error) {
 
 // Next returns nil errors every time there could be a new graph.
 func (obj *GAPI) Next() chan error {
-	if obj.data.NoWatch {
-		return nil
-	}
 	puppetChan := func() <-chan time.Time { // helper function
 		return time.Tick(time.Duration(RefreshInterval(obj.PuppetConf)) * time.Second)
 	}
@@ -93,7 +90,16 @@ func (obj *GAPI) Next() chan error {
 		}
 		startChan := make(chan struct{}) // start signal
 		close(startChan)                 // kick it off!
-		pChan := puppetChan()
+
+		pChan := make(<-chan time.Time)
+		// NOTE: we don't look at obj.data.NoConfigWatch since emulating
+		// puppet means we do not switch graphs on code changes anyways.
+		if obj.data.NoStreamWatch {
+			pChan = nil
+		} else {
+			pChan = puppetChan()
+		}
+
 		for {
 			select {
 			case <-startChan: // kick the loop once at start
@@ -108,7 +114,11 @@ func (obj *GAPI) Next() chan error {
 			}
 
 			log.Printf("Puppet: Generating new graph...")
-			pChan = puppetChan() // TODO: okay to update interval in case it changed?
+			if obj.data.NoStreamWatch {
+				pChan = nil
+			} else {
+				pChan = puppetChan() // TODO: okay to update interval in case it changed?
+			}
 			select {
 			case ch <- nil: // trigger a run (send a msg)
 			// unblock if we exit while waiting to send!