Properly close test http servers in unversioned

If not, using `go test -count=n` would make them pile up and ultimately
get to the limit of open files:

	client_test.go:522: expected an error, got Get http://127.0.0.1:46070/api: dial tcp 127.0.0.1:46070: socket: too many open files

Steps to reproduce (no longer fails):

	godep go test -short -run '^$' -o test .
	./test -test.run '^TestGetSwaggerSchema' -test.count 100

Note that this might not fail if your `ulimit -n` is not low enough.

pkg/client/unversioned/helper_test.go

@@ -185,6 +185,7 @@ func TestHelperGetServerAPIVersions(t *testing.T) {
 		w.WriteHeader(http.StatusOK)
 		w.Write(output)
 	}))
+	defer server.Close()
 	got, err := ServerAPIVersions(&Config{Host: server.URL, GroupVersion: &unversioned.GroupVersion{Group: "invalid version", Version: "one"}, Codec: testapi.Default.Codec()})
 	if err != nil {
 		t.Fatalf("unexpected encoding error: %v", err)