Adding an hdfs mode for the Scalding REPL

Added an ability to pass --hdfs and --local parameters to the ScaldingShell.

Users can now run the script as this:
```
USAGE: ./scripts/scald-repl.sh [hadoopGenericOptions]  [replOptions] --local | --hdfs
```

This is not backwards compatible with the earlier version of the REPL because the mode (--local or --hdfs) is required. This is consistent with the Tool inside scalding-core.