docker build locally because gcr.io/kustomize-functions/e2econtainerconfig doesn't exist in the public

Author: yutaroyamanaka

api/krusty/fnplugin_test.go

@@ -589,6 +589,9 @@ metadata:
       container:
         image: "gcr.io/kustomize-functions/e2econtainerconfig"
 `)
+	build := exec.Command("docker", "build", ".", "-t", "gcr.io/kustomize-functions/e2econtainerconfig")
+	build.Dir = "../../cmd/config/internal/commands/e2e/e2econtainerconfig"
+	assert.NoError(t, build.Run())
 	m := th.Run(tmpDir.String(), o)
 	actual, err := m.AsYaml()
 	assert.NoError(t, err)