coverage: need to see critical/assert logs in coverage builds

[mattklein123]

See discussion in #11784.

Right now if we hit an assert it's not clear because we only print the backtrace, due to:

envoy/.bazelrc

Line 132 in 3cc670d

coverage:test-coverage --test_arg="--log-path /dev/null"

We need to figure out a way to see more logs in coverage when things fail. cc @alyssawilk @antoniovicente @jmarantz @lizan