RS Needs to properly handle cases with mixed/multiple filesystems

As documented in RS-184, if RS is started with S3 as the default filesystem, it will fail if hdfs isn't started, due to an hdfs cache reader being started (even though it is obviously unnecessary in this case).

Even though we're about to write a patch to fix this issue, we still have yet to properly deal with using both hdfs and s3. https://gerrit.sjc.cloudera.com/#/c/13952/

Once this patch is in we'll have the scenario where the target filesystem=S3 can properly function without trying to access s3. RS will also work on s3 if the target filesystem is hdfs, but the s3 access keys have been properly set. This is somewhat confusing, ideally we would have some sort of variable that listed all of the running filesystems in the same place.