Add support for a backend_ratelimit_conf_path option in the
[filter:backend_ratelimit] config. If specified then the middleware
will give precedence to config options from that file over config
options from the [filter:backend_ratelimit] section.
The path defaults to /etc/swift/backend-ratelimit.conf.
The config file is periodically reloaded and any changed options are
applied. The middleware will log a warning the first time it fails to
load a config file that had previously been successfully loaded. The
middleware also logs at info level when it first successfully loads a
config file that had previously failed to be loaded. Otherwise, the
middleware will log when a config file is loaded that results in the
config being changed.
Change-Id: I6554e37c6ab5b0a260f99b54169cb90ab5718f81
e9abfd76ee