AttributeError NoneType exception from run_by_name if no analyzers are installed

[michaelweiser]

In a testing environment I have a Cortex in a Docker container that is still missing analysers. So the list of analysers returned by the API is empty. This causes the following exception when calling cortex4py.analyzers.run_by_name() with any name:

'NoneType' object has no attribute 'id'
Traceback (most recent call last):
  File "/home/m/PeekabooAV-Installer/PeekabooAV/peekaboo/ruleset/engine.py", line 193, in run
    result = rule.evaluate(sample)
  File "/home/m/PeekabooAV-Installer/PeekabooAV/peekaboo/ruleset/rules.py", line 754, in evaluate
    self.submit_to_cortex(sample, cortex_analyzer)
  File "/home/m/PeekabooAV-Installer/PeekabooAV/peekaboo/ruleset/rules.py", line 226, in submit_to_cortex
    job_id = self.cortex.submit(sample, analyzer)
  File "/home/m/PeekabooAV-Installer/PeekabooAV/peekaboo/toolbox/cortex.py", line 543, in submit
    job = self.api.analyzers.run_by_name(analyzer.name, params)
  File "/home/m/pd/lib/python3.8/site-packages/cortex4py/controllers/analyzers.py", line 89, in run_by_name
    return self.run_by_id(analyzer.id, observable, **kwargs)
AttributeError: 'NoneType' object has no attribute 'id'

I can handle the NoneType exception in my code but wanted to report the issue here in case you think it should rather be wrapped into a module-specific exception such as cortex4py.exceptions.NotFoundError or cortex4py.analyzers.run_by_name() signal error by e.g. returning None.

[nadouani]

I'll fix this using an extract from what has been committed in #22. thanks @michaelweiser