Fix k4run -l

[jmcarcell]

BEGINRELEASENOTES

• Fix k4run -l. Currently it fails because the parsing always wants a config file.

ENDRELEASENOTES

Current behavior (for example in the nightlies):

$ k4run -l
Error: missing gaudi options file.
Usage: k4run <options_file.py>, use --help to get a complete list of arguments

After this PR:

$ k4run -l
[k4run] Available components:
=====================
  AbortEventAlg (from GaudiExamples),
		 path: /Gaudi/install/python/GaudiExamples/__init__.py

  AlgContextAuditor (from GaudiAud),
		 path: /Gaudi/install/python/GaudiAud/__init__.py

  AlgContextSvc (from GaudiCommonSvc),
  ...

Passing no arguments keeps working as expected:

$ k4run
Error: missing gaudi options file.
Usage: k4run <options_file.py>, use --help to get a complete list of arguments

@atolosadelgado @BrieucF

[jmcarcell]

Merging to get this into the nightlies since it seems no one has any complaints about this and it fixed the issue for me