configure_auth_token_middleware was replaced by
configure_keystone_authtoken_middleware in
Id0dec1ba72467cce5cacfcfdb2bc0af2bd3a3610. Manila's
DevStack plugin no longer needs to create a cache
directory to use as the signing_dir for keystone
authtoken.
Change-Id: I18fa04e6c3a832e17ade3f84d8b43b15686f06fe