tests,stdlib,python: Add tests for base 10 to 2 SI unit check

**Note**: Erin needs to complete the commit by expanding this test to
properly test the behavior of this change.

To run the pyunit tests:

```sh
scons build/ALL/gem5.opt -j`nproc`
./build/ALL/gem5.opt tests/run_pyunit.py
```

Change-Id: I8cea0fe8b088e03e84072a000444953768bc3151

tests/pyunit/util/pyunit_convert_check.py

@@ -277,3 +277,11 @@ class ConvertTestSuite(unittest.TestCase):
         self.assertRaises(ValueError, conv, "-1K")
 
         self.assertEqual(conv("32F"), 273.15)
+
+    def test_base_10_to_2(self):
+        conv = convert._base_10_to_2
+
+        self.assertEqual(conv("1k"), "1Ki")
+        self.assertIsNone(conv("1Ki"))
+
+        # Leaving the rest of this test for Erin to finish.