Travis test fails to handle existing daemon running on 58900

[Cas]

Travis tests will occasionally fail if they find another daemon running on port 58900 and need the job restarting for it to pass.

The test code should handle another daemon running and choose another port but this is not working as there is no CannotListenError re-raised in daemon_entry.py. I couldn't see any quick fix so needs further investigation.

To replicate run:

deluged -p 58900
trial deluge.tests.test_json_api.JSONCustomUserTestCase.test_handle_request_auth_error

deluge.tests.test_json_api
  JSONCustomUserTestCase
    test_handle_request_auth_error ... 11:13:39.183 [ERROR   ][deluge.core.daemon_entry      :86  ] Cannot start deluged, listen port in use.
 Check for other running daemons or services using this port: localhost:58900
11:13:39.183 [INFO    ][deluge.core.daemon_entry      :94  ] Exiting...
 

STDERR: Exception raised:
STDERR:  Traceback (most recent call last):
STDERR:   File "<stdin>", line 8, in <module>
STDERR:   File "deluge/core/daemon_entry.py", line 98, in start_daemon
STDERR:     return run_profiled(run_daemon, options, output_file=options.profile, do_profile=options.profile)
STDERR:   File "deluge/common.py", line 1232, in run_profiled
STDERR:     return func(*args)
STDERR:   File "deluge/core/daemon_entry.py", line 87, in run_daemon
STDERR:     sys.exit(1)
STDERR: SystemExit: 1