Add tests for bluechi-is-online

[engelmi]

Please describe what you would like to see

In #962 the new package bluechi-is-online was introduced. However, adding integration tests was postponed since this new package is not part of the main components and we first need to be able to group integration tests better - this is done in #840.
Therefore, integration tests shall be added in the context of this issue as soon as #840 is solved.

Please describe the solution you'd like

Integration tests verifying that the bluechi-is-online tool is working as expected. A (not exhaustive) list of test cases:

• for bluechi-is-online agent
  • Add integration tests for bluechi-is-online agent without any cli options #981
  • only --wait=
  • only --monitor
  • --monitor and --switch-timeout=
  • --wait= and --monitor
  • --monitor, --wait and --switch-timeout=
• for bluechi-is-online node
  • Add integration tests for bluechi-is-online node without any cli options #982
  • only --wait=
  • only --monitor
  • --wait= and --monitor
• for bluechi-is-online system
  • without any cli options
  • only --wait=
  • only --monitor
  • --wait= and --monitor