title: pyspark : how to check if a file exists in hdfs
body: <p>I want to check if several files exist in hdfs before load them by SparkContext.
  I use pyspark. I tried 
  <code>os.system("hadoop fs -test -e %s" %path)</code>
  but as I have a lot of paths to check, the job crashed.
  I tried also <code>sc.wholeTextFiles(parent_path)</code> and then filter by keys. but it crashed also because the parent_path contains a lot of sub paths and files.
  Could you help me? </p>