Prevent extra snapshot with --use-new-run (#2943)

* Prevent extra snapshot when using new run

* Add unit tests for initializing snapshotter

There should be no snapshot for RunV2.  Added a test for SingleSnapshot
as well to prove that the test actually works (rather than `initialized`
just not being read or set properly).

pkg/executor/build.go

@@ -344,7 +344,7 @@ func (s *stageBuilder) build() error {
 	}
 
 	initSnapshotTaken := false
-	if s.opts.SingleSnapshot || s.opts.RunV2 {
+	if s.opts.SingleSnapshot {
 		if err := s.initSnapshotWithTimings(); err != nil {
 			return err
 		}