Added Hadoop HDFS FSImage exporter to list of exporters (#809)
Added Hadoop HDFS FSImage exporter to list of exporters (#809)

* Added Hadoop HDFS FSImage exporter to list of storage exporters

* Sorted storage exporters by name

ddfreyne/prometheus-docs,chosenken/docs,ddfreyne/prometheus-docs,chosenken/docs,du2016/prometheus-docs,ddfreyne/prometheus-docs,chosenken/docs,prometheus/docs,du2016/prometheus-docs,ddfreyne/prometheus-docs,chosenken/docs,prometheus/docs,prometheus/docs,du2016/prometheus-docs