Fix psycopg2 connection argument

commit 6eea97c3ef modified the kwarg from "user"
to "username" by mistake.

Change-Id: Idfe8425d08c065ef19e8952e8fcb205779243a99
Closes-Bug: #1689211

tooz/drivers/pgsql.py

@@ -220,7 +220,7 @@ class PostgresDriver(coordination.CoordinationDriver):
         dbname = options.get("dbname") or parsed_url.path[1:]
         kwargs = {}
         if parsed_url.username is not None:
-            kwargs["username"] = parsed_url.username
+            kwargs["user"] = parsed_url.username
         if parsed_url.password is not None:
             kwargs["password"] = parsed_url.password