Additional changes:
- removed unnecessary locking when initializing the exporter
cache map, as the service itself is responsible for locking.
- separated setupCache method into ClearExporterCache and
SetupExporterCache methods.
- removed idle ListenAndServe function that was only waiting for the
stopChan to close. The reload case was unreachable due to the reload
channel being created in Start instead of being passed down.
- removed Shutdown method on EventExporterS and replaced it with the
exported ClearExporterCache method as it provided the same
functionality.
