Fix style nits in p2p_compactblocks, make it easier to debug

Summary:
This diff fixes several nits found while doing D16474:

• Use the block hash as hex string in assert_equal. This is a bit slower but the debug.log shows the hash as hex string so it's much easier to debug via combine_logs.py
• Don't override the default timeout, this is uncessary and could introduce spurious failures
• Consistently use make_conform_to_ctor
• Fix a related but wrong comment in messages.py

Test Plan:

./test/functional/test_runner.py p2p_compactblocks

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16480