Fix kubeletstats logging and self reported metrics

[pmcollins]

Kubeletstats receiver was missing log statements on important errors and self-reported metrics was not working in lab.

Tested self-reported metrics by looking at prometheus endpoint at 8888.

[codecov]

Codecov Report

Merging #357 into master will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #357      +/-   ##
==========================================
+ Coverage   82.78%   82.83%   +0.04%     
==========================================
  Files         170      170              
  Lines        9070     9075       +5     
==========================================
+ Hits         7509     7517       +8     
+ Misses       1236     1234       -2     
+ Partials      325      324       -1     

Flag	Coverage Δ
#integration	0.00% <ø> (ø)
#unit	82.83% <100.00%> (+0.04%)	⬆️

Impacted Files	Coverage Δ
receiver/kubeletstatsreceiver/receiver.go	81.81% <100.00%> (ø)
receiver/kubeletstatsreceiver/runnable.go	100.00% <100.00%> (+13.04%)	⬆️

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[dmitryax]

Ifaik StartMetricsReceiveOp calls must always match with EndMetricsReceiveOp. So we shouldn't put EndMetricsReceiveOp under a condition. I don't think we need StartMetricsReceiveOp call here. We probably only need only one StartMetricsReceiveOp call and one EndMetricsReceiveOp call in this function, both of them should wrap err = r.consumer.ConsumeMetricsData(ctx, *md) in every iteration of the loop over MetricsData.

[pmcollins]

Agreed, will fix.