Add File-SD metrics (#2103)
Add File-SD metrics (#2103)

* Add File-SD metrics

* Count read errors, not scan errors.

PrFalken/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,agaoglu/prometheus,yanghongkjxy/prometheus,GoogleCloudPlatform/prometheus,Stackdriver/stackdriver-prometheus,keegancsmith/prometheus,PrFalken/prometheus,kzittritsch/prometheus,agaoglu/prometheus,yanghongkjxy/prometheus,tattsun/prometheus,keegancsmith/prometheus,AlekSi/prometheus,GoogleCloudPlatform/prometheus,Conorbro/prometheus,dsymonds/prometheus,slok/prometheus,Gouthamve/prometheus,SaltedMan/prometheus-annotated,datajet-io/prometheus,tomwilkie/prometheus,brancz/prometheus,Conorbro/prometheus,SaltedMan/prometheus-annotated,datajet-io/prometheus,kzittritsch/prometheus,kzittritsch/prometheus,tomwilkie/prometheus,GoogleCloudPlatform/prometheus,Colstuwjx/prometheus,amorken/prometheus,brancz/prometheus,prometheus/prometheus,keegancsmith/prometheus,JavierZunzunegui/prometheus,dsymonds/prometheus,tomwilkie/prometheus,brancz/prometheus,adamron1/prometheus,Stackdriver/stackdriver-prometheus,Stackdriver/stackdriver-prometheus,dsymonds/prometheus,prometheus/prometheus,alileza/prometheus,PrFalken/prometheus,dsymonds/prometheus,AlekSi/prometheus,amorken/prometheus,Conorbro/prometheus,gottwald/prometheus,Colstuwjx/prometheus,agaoglu/prometheus,prometheus/prometheus,amorken/prometheus,tattsun/prometheus,alileza/prometheus,adamron1/prometheus,JavierZunzunegui/prometheus,prometheus/prometheus,adamron1/prometheus,SaltedMan/prometheus-annotated,PrFalken/prometheus,alileza/prometheus,datajet-io/prometheus,slok/prometheus,gottwald/prometheus,Colstuwjx/prometheus,yanghongkjxy/prometheus,gottwald/prometheus,tomwilkie/prometheus,Stackdriver/stackdriver-prometheus,yanghongkjxy/prometheus,JavierZunzunegui/prometheus,Conorbro/prometheus,JavierZunzunegui/prometheus,slok/prometheus,keegancsmith/prometheus,amorken/prometheus,alileza/prometheus,AlekSi/prometheus,kangwoo/prometheus,kangwoo/prometheus,kzittritsch/prometheus,Gouthamve/prometheus,prometheus/prometheus,slok/prometheus,SaltedMan/prometheus-annotated,keegancsmith/prometheus,gottwald/prometheus,datajet-io/prometheus,tattsun/prometheus,adamron1/prometheus,brancz/prometheus,kangwoo/prometheus,Gouthamve/prometheus,agaoglu/prometheus,AlekSi/prometheus,Gouthamve/prometheus,tattsun/prometheus,kangwoo/prometheus,Colstuwjx/prometheus