Deprecate process supervisor collectors

Mark the `supervisord` and `systemd` as deprecated. These are process
supevisors like `runit` and out of scope for the node_exporter.

Signed-off-by: Ben Kochie <superq@gmail.com>

README.md

@@ -196,9 +196,7 @@ perf | Exposes perf based metrics (Warning: Metrics are dependent on kernel conf
 processes | Exposes aggregate process statistics from `/proc`. | Linux
 qdisc | Exposes [queuing discipline](https://en.wikipedia.org/wiki/Network_scheduler#Linux_kernel) statistics | Linux
 slabinfo | Exposes slab statistics from `/proc/slabinfo`. Note that permission of `/proc/slabinfo` is usually 0400, so set it appropriately. | Linux
-supervisord | Exposes service status from [supervisord](http://supervisord.org/). | _any_
 sysctl | Expose sysctl values from `/proc/sys`. Use `--collector.sysctl.include(-info)` to configure. | Linux
-systemd | Exposes service and system status from [systemd](http://www.freedesktop.org/wiki/Software/systemd/). | Linux
 tcpstat | Exposes TCP connection status information from `/proc/net/tcp` and `/proc/net/tcp6`. (Warning: the current version has potential performance issues in high load situations.) | Linux
 wifi | Exposes WiFi device and station statistics. | Linux
 zoneinfo | Exposes NUMA memory zone metrics. | Linux
@@ -211,6 +209,8 @@ Name     | Description | OS
 ---------|-------------|----
 ntp | Exposes local NTP daemon health to check [time](./docs/TIME.md) | _any_
 runit | Exposes service status from [runit](http://smarden.org/runit/). | _any_
+supervisord | Exposes service status from [supervisord](http://supervisord.org/). | _any_
+systemd | Exposes service and system status from [systemd](http://www.freedesktop.org/wiki/Software/systemd/). | Linux
 
 ### Perf Collector
 

collector/supervisord.go

@@ -69,6 +69,8 @@ func NewSupervisordCollector(logger log.Logger) (Collector, error) {
 		xrpc = xmlrpc.NewClient(*supervisordURL)
 	}
 
+	level.Warn(logger).Log("msg", "This collector is deprecated and will be removed in the next major version release.")
+
 	return &supervisordCollector{
 		upDesc: prometheus.NewDesc(
 			prometheus.BuildFQName(namespace, subsystem, "up"),

collector/systemd_linux.go

@@ -154,6 +154,8 @@ func NewSystemdCollector(logger log.Logger) (Collector, error) {
 	level.Info(logger).Log("msg", "Parsed flag --collector.systemd.unit-exclude", "flag", *unitExclude)
 	unitExcludePattern := regexp.MustCompile(fmt.Sprintf("^(?:%s)$", *unitExclude))
 
+	level.Warn(logger).Log("msg", "This collector is deprecated and will be removed in the next major version release.")
+
 	return &systemdCollector{
 		unitDesc:                      unitDesc,
 		unitStartTimeDesc:             unitStartTimeDesc,