[Testing] Fix random waiting in obi_test

[LucaRufer]

Fix the random waiting for the random manager and subordinate:

• The manager may only wait with receiving the response if the UseRReady feature is enabled. Otherwise, it always has to be ready to receive a response right away.
• Add the missing waits to the random subordinate. It may always wait a random amount of time with granting a request or providing a response.