Redefine swift configs in SWIFT_DIR

We still need a link in /etc/swift until #885595 is fixed.
diff --git a/files/swift/container-server.conf b/files/swift/container-server.conf
index 8d59bf2..bdc3e3a 100644
--- a/files/swift/container-server.conf
+++ b/files/swift/container-server.conf
@@ -4,6 +4,7 @@
 bind_port = %BIND_PORT%
 user = %USER%
 log_facility = LOG_LOCAL%LOG_FACILITY%
+swift_dir = %SWIFT_CONFIG_LOCATION%
 
 [pipeline:main]
 pipeline = container-server