Merge #12849: Tests: Add logging in loops in p2p_sendhears.py

Summary:
PR12849 backport https://github.com/bitcoin/bitcoin/pull/12849/files
8dd547d82b Adding logging for loop iteration level in p2p_sendheaders.py (ccdle12)

Pull request description:

PR for #12453

New contributor looking at mainly the 'good first issues'.

From my understanding of the issue:
 * Track the iteration level of loop when test fails in Travis CI

Further clarification on the issue would be greatly appreciated to narrow down what can be fixed or updated.

Depends on D3085

Test Plan: test_runner.py

Reviewers: jasonbcox, Fabien, #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Maniphest Tasks: T654

Differential Revision: https://reviews.bitcoinabc.org/D3086