Some tests access undefined `proto_var` variable

[mattst88]

These test scripts all contain a finally: block that attempts to print proto_ver which does not exist:

• test/broker/02-subpub-qos1-message-expiry.py
• test/broker/02-subpub-qos1-message-expiry-retain.py
• test/broker/02-subpub-qos1-message-expiry-will.py
• test/broker/02-subpub-qos2-pubrec-error.py

print("proto_ver=%d" % (proto_ver))

This mistake appears to be a copy-and-paste error in commit b2a9daf1 ("02 broker subpub tests with v5 support").

As a fix, I suggest:

1. s/proto_ver=5/proto_ver=proto_ver/g
2. s/do_test():/do_test(proto_ver):/g
3. s/do_test()/do_test(proto_ver=5)/g

I'd submit a patch, but the CLA process is too much for what is a single sed invocation.

sed -i \
    -e 's/proto_ver=5/proto_ver=proto_ver/g' \
    -e 's/do_test():/do_test(proto_ver):/g' \
    -e 's/do_test()/do_test(proto_ver=5)/g' \
    test/broker/02-subpub-qos1-message-expiry.py \
    test/broker/02-subpub-qos1-message-expiry-retain.py \
    test/broker/02-subpub-qos1-message-expiry-will.py \
    test/broker/02-subpub-qos2-pubrec-error.py