Error message not clear when the permission of staging dir is not as expected

SecureBulkLoadEndpoint checks the permission of staging dir. If it is not “rwxx-x”, the following error is prompted:

Directory already exists but permissions aren't set to '-rwx--x--x'

It says "Directory", but user has no idea what the directory is. User need to read code according to the stack trace to find that the error is for staging dir.
Need to add more info into the error message.

Master branch does not have this issue, as it does not check the permission any more.