pkg/gce: poll for operation completion less frequently

We are hitting quotas for operation completion polling.
Not surprising since we create/delete instances all the time.
Slightly decrease rate of polling.
diff --git a/pkg/gce/gce.go b/pkg/gce/gce.go
index e5194ae..0ba0c50 100644
--- a/pkg/gce/gce.go
+++ b/pkg/gce/gce.go
@@ -266,8 +266,9 @@
 }
 
 func (ctx *Context) waitForCompletion(typ, desc, opName string, ignoreNotFound bool) error {
+	time.Sleep(3 * time.Second)
 	for {
-		time.Sleep(2 * time.Second)
+		time.Sleep(3 * time.Second)
 		var op *compute.Operation
 		err := ctx.apiCall(func() (err error) {
 			switch typ {