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/interrupts_common.go

@@ -30,7 +30,7 @@ func init() {
 func NewInterruptsCollector() (Collector, error) {
 	return &interruptsCollector{
 		desc: typedDesc{prometheus.NewDesc(
-			namespace+"_interrupts",
+			namespace+"_interrupts_total",
 			"Interrupt details.",
 			interruptLabelNames, nil,
 		), prometheus.CounterValue},