Redefine swift configs in SWIFT_DIR

We still need a link in /etc/swift until #885595 is fixed.
diff --git a/files/swift/proxy-server.conf b/files/swift/proxy-server.conf
index 6b7dd52..fe7e39b 100644
--- a/files/swift/proxy-server.conf
+++ b/files/swift/proxy-server.conf
@@ -2,6 +2,7 @@
 bind_port = 8080
 user = %USER%
 log_facility = LOG_LOCAL1
+swift_dir = %SWIFT_CONFIG_LOCATION%
 
 [pipeline:main]
 pipeline = healthcheck cache %AUTH_SERVER% proxy-server