[avalanche] Also log when contenders are not promoted

Summary: The original log is very helpful for debugging functional tests, however we are left guessing what proofids are associated with contenders that were not promoted. This diff reuses that log and clearly indicates whether or not it was promoted.

Test Plan:

./test/functional/test_runner.py --nocleanup abc_p2p_avalanche_contender_voting

Inspect the log and see "was NOT promoted" log messages intermixed with "was promoted".

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18012