Add integration tests for bluechi-is-online node with --wait parameter

[mwperina]

Please describe what you would like to see

In #962 the new package bluechi-is-online was introduced. However, adding integration tests was postponed.

A basic integration test for bluechi-is-online node would verify that:

• It exits immediately with code 0 when the bluechi-agent is connected
• If bluechi-agent is not connected upon bluechi-is-online execution, bluechi-is-online waits with specified timeout and return 0 if bluechi-agent get connected within this timeout
• If bluechi-agent is not connected upon bluechi-is-online execution, bluechi-is-online waits with specified timeout and return non-zero if bluechi-agent doesn't get connected within this timeout

Tech hints

• To properly test --wait parameter you will need to run bluechi-is-online node in separate thread, for inspiration about using threads in integration tests you can take a look at https://github.com/eclipse-bluechi/bluechi/blob/main/tests/tests/tier0/bluechi-request-cancel/test_bluechi_request_cancel.py

[DanaOrr]

Please assign to me