SPARK-1795 - Add recursive directory file search to fileInputStream

Added recursive directory search to fileInputStream. Want spark to be able to find files in the subdirectories rather than just the parent directory. 
If the input directory is already the lowest level of directory then it will not consider any files in it.
example: 
Consider the following directory.
/a/file1.txt
/a/file2.txt and so on .
If the input directory is given as "/a", there will be no output.