Added an option to disable input path checking in hadoop

I've added a new option that disabled input path checking for the hadoop runner when set to `False`. This pull request also includes a change that uses `-ls` rather than `-stat` to check paths, as `-stat` throws an error if you have a path with a wildcard `*` in it.

The option is named `check_hadoop_input_paths` unsurprisingly.

Both of these are something we've required (partly for performance reasons), and figured it might be worth pushing upstream if it's something you feel worth including.