issue #587: 2.8 PlayContext lacks sudo_flags attribute.

This is a huge bodge.

ansible_mitogen/strategy.py

@@ -276,8 +276,8 @@ class StrategyMixin(object):
             class_only=True,
         )
         if play_context.connection is not Sentinel:
-            # 2.8 appears to defer computing this value until it's inside the
+            # 2.8 appears to defer computing this until inside the worker.
-            # worker. TODO: figure out where this value has moved.
+            # TODO: figure out where it has moved.
             ansible_mitogen.loaders.connection_loader.get(
                 name=play_context.connection,
                 class_only=True,

ansible_mitogen/transport_config.py

@@ -380,8 +380,9 @@ class PlayContextSpec(Spec):
             for term in ansible.utils.shlex.shlex_split(
                 first_true((
                     self._play_context.become_flags,
-                    self._play_context.sudo_flags,
+                    # Ansible <=2.7.
-                    # Ansible 2.3.
+                    getattr(self._play_context, 'sudo_flags', ''),
+                    # Ansible <=2.3.
                     getattr(C, 'DEFAULT_BECOME_FLAGS', ''),
                     getattr(C, 'DEFAULT_SUDO_FLAGS', '')
                 ), default='')