Dispatch the call to erase_block_device

There is no way for two hardware managers to handle erasing two disks
in two different ways. dispatch_to_managers was designed specifically
for this case, and the default behavior will remain the same for the
GenericHardwareManager (erase_block_device will pick up each disk).

Also return the result of the dispatch calls, so they'll be logged by
Ironic and give more cleaning insight.

Change-Id: I19e9dc8539a0729fbb96cae92fe633e24608fc68

ironic_python_agent/hardware.py

@@ -161,10 +161,15 @@ class HardwareManager(object):
 
         :param node: Ironic node object
         :param ports: list of Ironic port objects
+        :return: a dictionary in the form {device.name: erasure output}
         """
+        erase_results = {}
         block_devices = self.list_block_devices()
         for block_device in block_devices:
-            self.erase_block_device(node, block_device)
+            result = dispatch_to_managers(
+                'erase_block_device', node=node, block_device=block_device)
+            erase_results[block_device.name] = result
+        return erase_results
 
     def list_hardware_info(self):
         hardware_info = {}

ironic_python_agent/tests/unit/test_hardware.py

@@ -426,6 +426,22 @@ class TestGenericHardwareManager(test_base.BaseTestCase):
                 self.assertEqual(getattr(expected, attr),
                                  getattr(device, attr))
 
+    @mock.patch.object(hardware, 'dispatch_to_managers')
+    def test_erase_devices(self, mocked_dispatch):
+        mocked_dispatch.return_value = 'erased device'
+
+        self.hardware.list_block_devices = mock.Mock()
+        self.hardware.list_block_devices.return_value = [
+            hardware.BlockDevice('/dev/sdj', 'big', 1073741824, True),
+            hardware.BlockDevice('/dev/hdaa', 'small', 65535, False),
+        ]
+
+        expected = {'/dev/hdaa': 'erased device', '/dev/sdj': 'erased device'}
+
+        result = self.hardware.erase_devices({}, [])
+
+        self.assertEqual(expected, result)
+
     @mock.patch.object(utils, 'execute')
     def test_erase_block_device_ata_success(self, mocked_execute):
         hdparm_info_fields = {