Fix file descriptor leak in downloadFileExists()
Data export related changes

1. In DataCountService, when retrieving the patients in a patient set,
   do not use subject_sample_mapping in deapp. When DataCountService and
   PostgresDataCountService were collapsed into one,
   PostgresDataCountService was kept as DataCountService, but apparently
   it came from an older ancestry that did not have this fix.
2. Do not print errors to the log if no FTP server is set, just skip the
   FTP uploads/downloads.
3. Some refactoring and white space.

Related: FT-411