batchspawner/CondorSpawner: Make use of connect_to_job rport feature.

This uses the functionality to use a random local port on the hub
to forward the notebook port to. It ensures no port collisions
appear between different, forwarded notebooks.

batchspawner/batchspawner.py

@@ -908,7 +908,7 @@ class CondorSpawner(UserEnvMixin,BatchSpawnerRegexStates):
     # outputs job data XML string
     batch_query_cmd = Unicode('condor_q {job_id} -format "%s, " JobStatus -format "%s" RemoteHost -format "\n" True').tag(config=True)
     batch_cancel_cmd = Unicode('condor_rm {job_id}').tag(config=True)
-    connect_to_job_cmd = Unicode("condor_ssh_to_job -ssh \"ssh -L {port}:localhost:{port} -oExitOnForwardFailure=yes\" {job_id}").tag(config=True)
+    connect_to_job_cmd = Unicode("condor_ssh_to_job -ssh \"ssh -L {port}:localhost:{rport} -oExitOnForwardFailure=yes\" {job_id}").tag(config=True)
     # job status: 1 = pending, 2 = running
     state_pending_re = Unicode(r'^1,').tag(config=True)
     state_running_re = Unicode(r'^2,').tag(config=True)