Set default reader roles for Swift

Sets the default reader roles to SwiftSystemReader and
SwiftProjectReader, which align with the defaults from former TripleO
deployments. Customizing these needs to be done by overriding config
files using DefaultConfigOverwrite.

templates/swiftproxy/config/proxy-server.conf

@@ -66,6 +66,8 @@ use = egg:swift#keystoneauth
 operator_roles = admin, SwiftOperator
 cache = swift.cache
 reseller_prefix=AUTH_
+system_reader_roles = SwiftSystemReader
+project_reader_roles = SwiftProjectReader
 
 [filter:authtoken]
 paste.filter_factory = keystonemiddleware.auth_token:filter_factory