bootconfig: fix get_current_bcd_store for PyMI

When PyMI replaced the WMI implementation, the method contract for
`conn.BcdStore.OpenStore` changed, leading to an error:

```bash
ValueError: not enough values to unpack (expected 2, got 1)
```

Under PyMI, the following returns one element if the store is found,
two elements otherwise:

```python
>> conn.BcdStore.OpenStore(File="fake")
(False, None)
>> conn.BcdStore.OpenStore(File="")
(<pymi_object: >,)
```

Fixes: #146

Change-Id: Ibb298e4c92c451946a3ac4cfd2e436b2b3c203cf
Signed-off-by: Adrian Vladu <avladu@cloudbasesolutions.com>

Author: ader1990

cloudbaseinit/tests/utils/windows/test_bootconfig.py

@@ -84,23 +84,25 @@ def test_get_boot_system_devices(self):
             **expected_call_args)
         self.assertEqual(res, [mock_id])
 
-    def _test_get_current_bcd_store(self, mock_success=True, mock_store=None):
+    def _test_get_current_bcd_store(self, mock_success=True):
         conn = self._wmi_mock.WMI
-        store = self._wmi_mock._wmi_object
-        mock_store = mock.Mock()
         mock_bcdstore = mock.MagicMock()
         conn.return_value = mock_bcdstore
-        store.return_value = mock_store
-        mock_bcdstore.BcdStore.OpenStore.return_value = (mock_success,
-                                                         mock_store)
+        mock_store_open_store = mock.MagicMock()
+        mock_store_open_object = mock.MagicMock()
+        mock_bcdstore.BcdStore.OpenStore.return_value = (
+            mock_store_open_store, None)
         if not mock_success:
+            mock_bcdstore.BcdStore.OpenStore.return_value = (False, None)
             self.assertRaises(
                 exception.CloudbaseInitException,
                 self.bootconfig._get_current_bcd_store)
         else:
-            mock_store.OpenObject.return_value = [None, mock_success]
+            mock_store_open_store.OpenObject.return_value = [
+                mock_store_open_object,
+                None]
             res_store = self.bootconfig._get_current_bcd_store()
-            self.assertEqual(res_store, mock_store)
+            self.assertEqual(res_store, mock_store_open_object)
 
     def test_get_current_bcd_store(self):
         self._test_get_current_bcd_store()

cloudbaseinit/utils/windows/bootconfig.py

@@ -56,13 +56,19 @@ def get_boot_system_devices():
 
 def _get_current_bcd_store():
     conn = wmi.WMI(moniker='//./root/wmi')
-    success, store = conn.BcdStore.OpenStore(File="")
-    if not success:
+    # Under PyMI, the following returns one element if the store is found,
+    # two elements otherwise.
+    #
+    #     >>> conn.BcdStore.OpenStore(File="file not present")
+    #    (False, None)
+    #    >>> conn.BcdStore.OpenStore(File="")
+    #    (<pymi_object: >,)
+    store = conn.BcdStore.OpenStore(File="")[0]
+    if not store:
         raise exception.CloudbaseInitException("Cannot open BCD store")
-    store = wmi._wmi_object(store)
-    current_store, success = store.OpenObject(Id=STORE_CURRENT)
-    current_store = wmi._wmi_object(current_store)
-    if not success:
+
+    current_store = store.OpenObject(Id=STORE_CURRENT)[0]
+    if not current_store:
         raise exception.CloudbaseInitException("Cannot open BCD current store")
 
     return current_store