Baker/Test: fix keep-alive test for baker

What

Fixes the test (we could say improve as it was mostly passing)

Why

The test with remote node from !17786 (merged) exhibited that the test was incorrect, it has nothing to do with remote node but the test was failing.

How

Events were not properly handled, I created one promise wait_for_period_status, but I waited a second time on a resolved promise, which is a no-op. Additionally, the test creates event before the baker is up and ready, therefore I added an additional event, if the baker can retrieve the chain id, we know it's connected to the node.

Manually testing the MR

tezt -f agnostic_baker_test.ml keep_alive -j 5

and more importantly what was failing:

 TZ_SCHEDULE_KIND=EXTENDED_BAKER_REMOTE_MODE_TESTS tezt -f agnostic_baker_test.ml keep_alive -j 5

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR