Handle nova instance having no image

There will be no image when the instance boots from volume. In the
future there could be a fallback to fetch the metadata from the volume
but for now just return None for boot mode and secure boot.

Change-Id: I00576ee19571bd91683fd6c1754e0624e469b2c9

sushy_tools/emulator/resources/systems/novadriver.py

@@ -85,6 +85,8 @@ class OpenStackDriver(AbstractSystemsDriver):
 
     @memoize.memoize(permanent_cache=PERMANENT_CACHE)
     def _get_image_info(self, identity):
+        if not identity:
+            return
         return self._cc.image.find_image(identity)
 
     def _get_server_metadata(self, identity):

sushy_tools/tests/unit/emulator/resources/systems/test_nova.py

@@ -155,6 +155,16 @@ class NovaDriverTestCase(base.BaseTestCase):
 
         self.assertEqual('Legacy', boot_mode)
 
+    def test_get_boot_mode_no_image(self):
+        server = mock.Mock(id=self.uuid, image=dict(id=self.uuid))
+        self.nova_mock.return_value.get_server.return_value = server
+
+        self.nova_mock.return_value.image.find_image.return_value = None
+
+        boot_mode = self.test_driver.get_boot_mode(self.uuid)
+
+        self.assertIsNone(boot_mode)
+
     def test_set_boot_mode(self):
         self.assertRaises(
             error.FishyError, self.test_driver.set_boot_mode,