Maintaining downtime on Icinga2 fragile

[stdevel]

Describe the bug
Scheduling downtimes on Icinga2 works, but katprep crashes with an BadStatusLine error.

To Reproduce
Steps to reproduce the behavior:

1. Schedule downtime, e.g.: katprep_maintenance *.json prepare
2. See error

Expected behavior
Downtime should be scheduled without crashing katprep.

Screenshots
If applicable, add screenshots to help explain your problem.

Environment (please complete the following information):

• OS version: CentOS 7.5
• Red Hat Satellite or Foreman/Katello version: 1.19.0/3.8.0
• Icinga2 version: 2.8.4-1

Additional context
Could also be an upstream issue: Icinga/icinga2#6635

Stacktrace:

$ katprep_maintenance -C katprep.auth 
  File "/usr/local/bin/katprep_maintenance", line 11, in <module>
    load_entry_point('katprep==0.5.0', 'console_scripts', 'katprep_maintenance')()
  File "build/bdist.linux-x86_64/egg/katprep/maintenance.py", line 884, in cli
  File "build/bdist.linux-x86_64/egg/katprep/maintenance.py", line 863, in main
  File "build/bdist.linux-x86_64/egg/katprep/maintenance.py", line 251, in prepare
  File "build/bdist.linux-x86_64/egg/katprep/maintenance.py", line 196, in manage_host_preparation
  File "build/bdist.linux-x86_64/egg/katprep/clients/Icinga2APIClient.py", line 278, in schedule_downtime
  File "build/bdist.linux-x86_64/egg/katprep/clients/Icinga2APIClient.py", line 248, in __manage_downtime
  File "build/bdist.linux-x86_64/egg/katprep/clients/Icinga2APIClient.py", line 160, in __api_post
  File "build/bdist.linux-x86_64/egg/katprep/clients/Icinga2APIClient.py", line 118, in __api_request
  File "/home/vagrant/.local/lib/python2.7/site-packages/requests/sessions.py", line 559, in post
    return self.request('POST', url, data=data, json=json, **kwargs)
  File "/home/vagrant/.local/lib/python2.7/site-packages/requests/sessions.py", line 512, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/vagrant/.local/lib/python2.7/site-packages/requests/sessions.py", line 622, in send
    r = adapter.send(request, **kwargs)
  File "/home/vagrant/.local/lib/python2.7/site-packages/requests/adapters.py", line 495, in send
    raise ConnectionError(err, request=request)
requests.exceptions.ConnectionError: ('Connection aborted.', BadStatusLine("''",))

[stdevel]

Received the hint, that the API is not designed for serving multiple requests in one session. So the workaround would be to close the API session after every request and re-establish it afterwards.