Take into account the server-side inventory for local diff

If implemented users will be able to use a local kustomization file while
retrieving status from the live kustomization file.

Signed-off-by: Soule BA <soule@weave.works>
(cherry picked from commit 90d95988aa)

cmd/flux/build_kustomization_test.go

@@ -159,6 +159,7 @@ spec:
 	tmpl := map[string]string{
 		"fluxns": allocateNamespace("flux-system"),
 	}
+	setup(t, tmpl)
 
 	testEnv.CreateObjectFile("./testdata/build-kustomization/podinfo-source.yaml", tmpl, t)