rework the integration tests

[bodsch]

I would like to revise the integration tests in the long term. Changes in this PR:

• the graylog container is no longer fetched from the registry, but the locally available data is used
• integration of another API call to integrate roles
  • some more structure in integration_test.sh

My plan for the future:

• more API calls (maybe add / delete a dashboard)
• possibly an LDAP connection
• more ideas are welcome

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1 out of 2 committers have signed the CLA.

:white_check_mark: bodsch
:x: Bodo Schulz

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[bodsch]

sorry, i have trouble with my commits. I'll abort and post a new PR