[options] Correctly hide login info from debug outputs (#13696)

Iterate over opts instead of PRIVATE_OPTS for both performance and
correctness

test/test_options.py

@@ -0,0 +1,26 @@
+# coding: utf-8
+
+from __future__ import unicode_literals
+
+# Allow direct execution
+import os
+import sys
+import unittest
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from youtube_dl.options import _hide_login_info
+
+
+class TestOptions(unittest.TestCase):
+    def test_hide_login_inf(self):
+        self.assertEqual(_hide_login_info(['-u', 'foo', '-p', 'bar']),
+                         ['-u', 'PRIVATE', '-p', 'PRIVATE'])
+        self.assertEqual(_hide_login_info(['-u']), ['-u'])
+        self.assertEqual(_hide_login_info(['-u', 'foo', '-u', 'bar']),
+                         ['-u', 'PRIVATE', '-u', 'PRIVATE'])
+        self.assertEqual(_hide_login_info(['--username=foo']),
+                         ['--username=PRIVATE'])
+
+
+if __name__ == '__main__':
+    unittest.main()