IF: Fix LIB advancement detection in IF transition tests

[linh2931]

Occasionally votes_greater_than_threshold_test fails in CICD. The issue was votes are signed asynchronously and they could be delayed. The test only waited for 4 blocks to decide whether LIB had advanced. On a busy test machine, this could be insufficient.

• Increased the number of blocks waited for LIB advancing to 50.
• Moved finality transition related tests from api_tests.cpp to finality_transition_tests.cpp.

Resolved #2267

[ericpassmore]

Note:start
group: IF
category: CLOSED
summary: Closed. Changes to ensure enough asynchronous votes are received to advance LIB in tests.
Note:end

[heifner]

Seems to me we need something like wait_for_vote or ability to run controller in test mode where it votes synchronously.

[linh2931]

I thought about using conditional variable to wait. That amounts to the same we are doing now -- checking LIB in a loop and and breaking if it advances. If using controller to vote synchronously, that does not test the actual voting. Tests in finality_tests.cpp vote synchronously.
I think if after a large number of blocks LIB still does not advance, something must be wrong; tests here can catch that.

[arhag]

Closing since the proper solution is tracked by #2289.