chimney script: add a prompt before deleting the previous blobber

currently, when a user runs chimney script, and if there any previous blobber its data will be erased without warning. 


We if there is a previous blobber deployment, we should prompt the user and show a warning telling: 
"A blobber already exists on this server. Do you wish to delete blobber currently deployed on this server [N/y]:"