Make metrics better follow guidelines (#787)

* Improve stat linux metric names.

cpu is no longer used.

* node_cpu -> node_cpu_seconds_total for Linux

* Improve filesystem metric names with units

* Improve units and names of linux disk stats

Remove sector metrics, the bytes metrics cover those already.

* Infiniband counters should end in _total

* Improve timex metric names, convert to more normal units.

See
3c073991eb/kernel/time/ntp.c (L909)
for what stabil means, looks like a moving average of some form.

* Update test fixture

* For meminfo metrics that had "kB" units, add _bytes

* Interrupts counter should have _total

collector/cpu_linux.go

@@ -54,7 +54,7 @@ func init() {
 func NewCPUCollector() (Collector, error) {
 	return &cpuCollector{
 		cpu: prometheus.NewDesc(
-			prometheus.BuildFQName(namespace, "", cpuCollectorSubsystem),
+			prometheus.BuildFQName(namespace, cpuCollectorSubsystem, "seconds_total"),
 			"Seconds the cpus spent in each mode.",
 			[]string{"cpu", "mode"}, nil,
 		),