E2E: Add missing Bootstrap() call

One of the vsphere storage test suites was hitting a nil panic because
it did not call Bootstrap().

test/e2e/storage/vsphere/vsphere_stress.go

@@ -57,6 +57,7 @@ var _ = utils.SIGDescribe("vsphere cloud provider stress [Feature:vsphere]", fun
 
 	ginkgo.BeforeEach(func() {
 		framework.SkipUnlessProviderIs("vsphere")
+		Bootstrap(f)
 		client = f.ClientSet
 		namespace = f.Namespace.Name