Centralise Controller Queue and Worker processing

There were multiple places where queue and worker
goroutines pattern for controllers (and related) were
repeated in almost exactly the same ways.

Since there are more controllers coming, it made sense
to consolidate this logic into a centralised place that
could be reused to make authoring them easier.

This may also allow us to centralise some health checking in #98

pkg/gameservers/sdkserver.go

@@ -20,6 +20,7 @@ import (
 	"strings"
 	"sync"
 	"time"
+	"strings"
 
 	"agones.dev/agones/pkg/apis/stable"
 	stablev1alpha1 "agones.dev/agones/pkg/apis/stable/v1alpha1"