Add database config class (#6513)

This encapsulates config for a given database and is the way to get new
connections.

tests/replication/slave/storage/_base.py

@@ -20,7 +20,7 @@ from synapse.replication.tcp.client import (
     ReplicationClientHandler,
 )
 from synapse.replication.tcp.resource import ReplicationStreamProtocolFactory
-from synapse.storage.database import Database
+from synapse.storage.database import make_conn
 
 from tests import unittest
 from tests.server import FakeTransport
@@ -41,10 +41,12 @@ class BaseSlavedStoreTestCase(unittest.HomeserverTestCase):
 
     def prepare(self, reactor, clock, hs):
 
+        db_config = hs.config.database.get_single_database()
         self.master_store = self.hs.get_datastore()
         self.storage = hs.get_storage()
+        database = hs.get_datastores().databases[0]
         self.slaved_store = self.STORE_TYPE(
-            Database(hs), self.hs.get_db_conn(), self.hs
+            database, make_conn(db_config, database.engine), self.hs
         )
         self.event_id = 0