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 given directory contains both files and directories then the files will be ignored and only lowest level of subdirectories will be considered.
Example:
If the input directory has following structure.
/input/directory/\<files>
/input/directory/\<directories>

And if the data that to be considered is available in files in "/input/directory/" then it will be ignored.