MM-27744 disable Zap for unit tests. (#15398)

MM-27744 disable Zap for unit tests.

Zap has no concept of shutdown or close. Zap is only shutdown when the app exits. Not a problem for console logging, but when creating a new Zap logger that outputs to files on every unit test, that leaves no easy way to clean up until process exit. Depending on what else is running this can exhaust all file handles and cause unit tests to fail.

Zap is now disabled unit tests and uses Logr instead, regardless of config settings. `make test-server` peak file handle usage dropped from ~5K to less than 100.

mlog/default.go

@@ -76,12 +76,18 @@ func defaultAdvancedShutdown(ctx context.Context) error {
 	return nil
 }
 
-func defaultAddTarget(target logr.Target) error {
+func defaultAddTarget(targets ...logr.Target) error {
 	// mlog.AddTarget should not be called until default
 	// logger is replaced with mlog.Logger instance.
 	return errors.New("cannot AddTarget on default logger")
 }
 
+func defaultRemoveTargets(ctx context.Context, f func(TargetInfo) bool) error {
+	// mlog.RemoveTargets should not be called until default
+	// logger is replaced with mlog.Logger instance.
+	return errors.New("cannot RemoveTargets on default logger")
+}
+
 func defaultEnableMetrics(collector logr.MetricsCollector) error {
 	// mlog.EnableMetrics should not be called until default
 	// logger is replaced with mlog.Logger instance.