Add synchronous call to EventHub.shared.start() for use in testing

[kevinlind]

Task description

Improve performance and stability of unit tests which make use of the EventHub by adding a synchronous call to EventHub.shared.start() to allow test cases ensure the EventHub has started before running tests.
The Edge extension's EdgePublicAPITests were failing because calls to registerEventListener were failing presumably because the EventHub wasn't fully started. Adding a sleep() call after calling start() resolves the issue, but getting a signal from the EventHub when start() completes is a better option. Searching the repos shows several extensions call EventHub.shared.start() from unit tests, though I'm not aware of over test failures.

Additional implementation details or code snippet(s)

No response