Add a cancel_and_await() utility function

This is a very common pattern when cancelling a task.

This also introduces a new package `util` and a module `asyncio` inside
of it.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

src/frequenz/sdk/util/__init__.py

@@ -0,0 +1,4 @@
+# License: MIT
+# Copyright © 2022 Frequenz Energy-as-a-Service GmbH
+
+"""General purpose tools."""

src/frequenz/sdk/util/asyncio.py

@@ -0,0 +1,21 @@
+# License: MIT
+# Copyright © 2022 Frequenz Energy-as-a-Service GmbH
+
+"""General purpose async tools."""
+
+import asyncio
+
+
+async def cancel_and_await(task: asyncio.Task) -> None:
+    """Cancel a task and wait for it to finish.
+
+    The `CancelledError` is suppresed, but any other exception will be propagated.
+
+    Args:
+        task: The task to be cancelled and waited for.
+    """
+    task.cancel()
+    try:
+        await task
+    except asyncio.CancelledError:
+        pass