test: Wait for 'cmpctblock' in p2p_compactblocks when it is expected

Summary:
This is a more narrowly-construed wait which eliminates the possibility of the
wait being triggered by other messages.

Co-authored-by: Billy Garrison <billygarrison.btc@gmail.com>

This is a backport of core#19631

Test Plan: test/functional/test_runner.py p2p_compa*

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D10065