Close monitoring processes at shutdown, freeing some fds

Before this PR, pytest parsl/tests/test_monitoring/ leaves 1093 fds open
(which is too much for the test suite to complete in some default
configurations of max fds 1024)

After this PR, that test run leaves 895 fds open.

parsl/monitoring/monitoring.py

@@ -244,6 +244,7 @@ def close(self) -> None:
             self.router_exit_event.set()
             logger.info("Waiting for router to terminate")
             self.router_proc.join()
+            self.router_proc.close()
             logger.debug("Finished waiting for router termination")
             if len(exception_msgs) == 0:
                 logger.debug("Sending STOP to DBM")
@@ -252,13 +253,15 @@ def close(self) -> None:
                 logger.debug("Not sending STOP to DBM, because there were DBM exceptions")
             logger.debug("Waiting for DB termination")
             self.dbm_proc.join()
+            self.dbm_proc.close()
             logger.debug("Finished waiting for DBM termination")
 
             # should this be message based? it probably doesn't need to be if
             # we believe we've received all messages
             logger.info("Terminating filesystem radio receiver process")
             self.filesystem_proc.terminate()
             self.filesystem_proc.join()
+            self.filesystem_proc.close()
 
             logger.info("Closing monitoring multiprocessing queues")
             self.exception_q.close()