update webhdfs names, add validation
update webhdfs names, add validation

1) WebHDFS method names updated to be in sync with Esri/webhdfs-py
2) 'webhdfs' variable renamed to 'wh' for clarity (not to be confused
with package name
3) file existance is checked in CopyToHDFS.updateMessages

Esri/spatial-framework-for-hadoop,justvarshney/spatial-framework-for-hadoop,komamitsu/spatial-framework-for-hadoop,gisfromscratch/spatial-framework-for-hadoop