Get latest file from ftp

[jacobdadams]

From @steveoh:

Two other use cases we've had for this are, download all the csv's in a directory and download this specific file. It would be nice to provide some metadata about the file from the sftp as well since one of those use cases stored the modified date and would compare it to the last run to ensure it wasn't loading the same data twice.

remote_mtime = sftp.stat(file_path).st_mtime

if remote_mtime > mtime:
    self.log.debug('downloading {}'.format(file_path))
    sftp.get(file_path, local_path, preserve_mtime=True)

    return True