HPCC-11698 WARNING: Remote file connect Too many open files

Roxie was leaving sockets open for remote files that it has checked the
existance of but not actually opened. These were not covered by the code that
limits the number of remote files in use (since Roxie did not consider them to
be in use...)

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6098 from richardkchapman/roxie-remote-file-handles

HPCC-11698 WARNING: Remote file connect Too many open files

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>