Fix OSError catch

The _execute helper was catching OSError, except it
was expecting the same attributes as ProcessExecutionError,
which is incorrect.

Added a separate catch and unit test to ensure that we
at least properly catch and convert the error instead of
raising an error about an attribute that does not exist.

Change-Id: Id47715a5657478e4d9dd10ea7f360b1ededa27de
Closes-Bug: #1715466

ironic_python_agent/extensions/iscsi.py

@@ -36,10 +36,14 @@ DEFAULT_ISCSI_PORTAL_PORT = 3260
 def _execute(cmd, error_msg, **kwargs):
     try:
         stdout, stderr = utils.execute(*cmd, **kwargs)
-    except (processutils.ProcessExecutionError, OSError) as e:
+    except processutils.ProcessExecutionError as e:
         LOG.error(error_msg)
         raise errors.ISCSICommandError(error_msg, e.exit_code,
                                        e.stdout, e.stderr)
+    except OSError as e:
+        LOG.error("Error: %(error)s: OS Error: %(os_error)s",
+                  {'error': error_msg, 'os_error': e})
+        raise errors.ISCSICommandError(e, e.errno, None, None)
 
 
 def _wait_for_tgtd(attempts=10):

ironic_python_agent/tests/unit/extensions/test_iscsi.py

@@ -134,6 +134,15 @@ class TestISCSIExtensionTgt(test_base.BaseTestCase):
         mock_execute.assert_has_calls(expected)
         mock_dispatch.assert_called_once_with('get_os_install_device')
 
+    def test_start_iscsi_target_fail_command_not_exist(self, mock_execute,
+                                                       mock_dispatch,
+                                                       mock_destroy):
+        mock_dispatch.return_value = self.fake_dev
+        mock_execute.side_effect = OSError('file not found')
+        self.assertRaises(errors.ISCSIError,
+                          self.agent_extension.start_iscsi_target,
+                          iqn=self.fake_iqn)
+
 
 _ORIG_UTILS = iscsi.rtslib_fb.utils