resources: Simplify resource Converger and Startup code

This takes the Converged initialization and Startup patterns that are
common in all resources, and bakes it into the core engine. This way
resource writing is much more concise and there is less boilerplate!

resources/resources.go

@@ -130,6 +130,9 @@ type Base interface {
 	AssociateData(*Data)
 	IsWatching() bool
 	SetWatching(bool)
+	RegisterConverger()
+	UnregisterConverger()
+	Converger() converger.ConvergerUID
 	GetState() ResState
 	SetState(ResState)
 	DoSend(chan event.Event, string) (bool, error)
@@ -147,6 +150,7 @@ type Base interface {
 	GetGroup() []Res    // return everyone grouped inside me
 	SetGroup([]Res)
 	VarDir(string) (string, error)
+	Running(chan event.Event) error // notify the engine that Watch started
 }
 
 // Res is the minimum interface you need to implement to define a new resource.
@@ -171,7 +175,8 @@ type BaseRes struct {
 	kind      string
 	events    chan event.Event
 	converger converger.Converger // converged tracking
-	prefix    string              // base prefix for this resource
+	cuid      converger.ConvergerUID
+	prefix    string // base prefix for this resource
 	debug     bool
 	state     ResState
 	watching  bool  // is Watch() loop running ?
@@ -285,6 +290,24 @@ func (obj *BaseRes) SetWatching(b bool) {
 	obj.watching = b
 }
 
+// RegisterConverger sets up the cuid for the resource. This is a helper
+// function for the engine, and shouldn't be called by the resources directly.
+func (obj *BaseRes) RegisterConverger() {
+	obj.cuid = obj.converger.Register()
+}
+
+// UnregisterConverger tears down the cuid for the resource. This is a helper
+// function for the engine, and shouldn't be called by the resources directly.
+func (obj *BaseRes) UnregisterConverger() {
+	obj.cuid.Unregister()
+}
+
+// Converger returns the ConvergerUID for the resource. This should be called
+// by the Watch method of the resource to set the converged state.
+func (obj *BaseRes) Converger() converger.ConvergerUID {
+	return obj.cuid
+}
+
 // GetState returns the state of the resource.
 func (obj *BaseRes) GetState() ResState {
 	return obj.state