Port synapse_port_db to async/await (#6718)

* Raise an exception if there are pending background updates

So we return with a non-0 code

* Changelog

* Port synapse_port_db to async/await

* Port update_database to async/await

* Add version string to mocked homeservers

* Remove unused imports

* Convert overseen bits to async/await

* Fixup logging contexts

* Fix imports

* Add a way to print an error without raising an exception

* Incorporate review

changelog.d/6718.bugfix

@@ -0,0 +1 @@
+Fix a bug causing the `synapse_port_db` script to return 0 in a specific error case.

scripts-dev/update_database

@@ -22,10 +22,12 @@ import yaml
 
 from twisted.internet import defer, reactor
 
+import synapse
 from synapse.config.homeserver import HomeServerConfig
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.server import HomeServer
 from synapse.storage import DataStore
+from synapse.util.versionstring import get_version_string
 
 logger = logging.getLogger("update_database")
 
@@ -38,6 +40,8 @@ class MockHomeserver(HomeServer):
             config.server_name, reactor=reactor, config=config, **kwargs
         )
 
+        self.version_string = "Synapse/"+get_version_string(synapse)
+
 
 if __name__ == "__main__":
     parser = argparse.ArgumentParser(
@@ -81,15 +85,17 @@ if __name__ == "__main__":
     hs.setup()
     store = hs.get_datastore()
 
-    @defer.inlineCallbacks
-    def run_background_updates():
-        yield store.db.updates.run_background_updates(sleep=False)
+    async def run_background_updates():
+        await store.db.updates.run_background_updates(sleep=False)
         # Stop the reactor to exit the script once every background update is run.
         reactor.stop()
 
-    # Apply all background updates on the database.
-    reactor.callWhenRunning(
-        lambda: run_as_background_process("background_updates", run_background_updates)
-    )
+    def run():
+        # Apply all background updates on the database.
+        defer.ensureDeferred(
+            run_as_background_process("background_updates", run_background_updates)
+        )
+
+    reactor.callWhenRunning(run)
 
     reactor.run()