[avalanche] Fix potential failure in abc_p2p_avalanche_proof_voting

Summary:
On rare occasion (about 1/1000 run on my machine), the test will fail to find the vote finalization message in the log, because we don't keep sending the vote over the timeout period. This diff uses a retry mechanism to work around this.

Because the default timeout for assert_debug_log is 2s and there are 5 retries, the total timeout is slightly bumped to 12s which is not significant.

Test Plan:

for i in {1..10000}; do echo "Trial number $i" && ./test/functional/test_runner.py abc_p2p_avalanche_proof_voting || break; done

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D11089