Catch2Tests: Improve TestServer core dump handling

Currently, if our TestServer crashes the test doesn't notice and the coredump isn't printed because of a bug in ci/print-coredumps.sh.

I have also included some commits to make sure the test_test_server.cpp tests log the server output properly.

This MR fixes both of these issues. This needs to be merged after !1294 (merged) as I started from there as I was touching the same code.