Move _is_mapping to more central location

The logic to identify volumes is currently a nested function
in _default_block_device_names, named _is_mapping. It should
be moved to a more general location so others could utilize it
and allow it to be properly unit tested. The following patch
moves _is_mapping to nova/virt/block_device.py and renames it
to is_block_device_mapping.

Change-Id: I560abc4b57ca5bd195282af7cd1ab9bbf7600b67
Closes-Bug: #1351810

nova/compute/manager.py

@@ -1693,16 +1693,12 @@ class ComputeManager(manager.Manager):
         if update_root_bdm:
             root_bdm.save()
 
-        def _is_mapping(bdm):
-            return (bdm.source_type in ('image', 'volume', 'snapshot', 'blank')
-                    and bdm.destination_type == 'volume'
-                    and driver_block_device.is_implemented(bdm))
-
         ephemerals = filter(block_device.new_format_is_ephemeral,
                             block_devices)
         swap = filter(block_device.new_format_is_swap,
                       block_devices)
-        block_device_mapping = filter(_is_mapping, block_devices)
+        block_device_mapping = filter(
+              driver_block_device.is_block_device_mapping, block_devices)
 
         self._default_device_names_for_instance(instance,
                                                 root_device_name,

nova/tests/virt/test_block_device.py

@@ -666,3 +666,19 @@ class TestDriverBlockDevice(test.NoDBTestCase):
         local_image = self.image_bdm.copy()
         local_image['destination_type'] = 'local'
         self.assertFalse(driver_block_device.is_implemented(local_image))
+
+    def test_is_block_device_mapping(self):
+        test_swap = self.driver_classes['swap'](self.swap_bdm)
+        test_ephemeral = self.driver_classes['ephemeral'](self.ephemeral_bdm)
+        test_image = self.driver_classes['image'](self.image_bdm)
+        test_snapshot = self.driver_classes['snapshot'](self.snapshot_bdm)
+        test_volume = self.driver_classes['volume'](self.volume_bdm)
+        test_blank = self.driver_classes['blank'](self.blank_bdm)
+
+        for bdm in (test_image, test_snapshot, test_volume, test_blank):
+            self.assertTrue(driver_block_device.is_block_device_mapping(
+                bdm._bdm_obj))
+
+        for bdm in (test_swap, test_ephemeral):
+            self.assertFalse(driver_block_device.is_block_device_mapping(
+                bdm._bdm_obj))

nova/virt/block_device.py

@@ -466,3 +466,9 @@ def is_implemented(bdm):
         except _NotTransformable:
             pass
     return False
+
+
+def is_block_device_mapping(bdm):
+    return (bdm.source_type in ('image', 'volume', 'snapshot', 'blank')
+            and bdm.destination_type == 'volume'
+            and is_implemented(bdm))