Server/client test is flaky

[MichaelGrupp]

This already has a TODO note in the code, but I think it's good to keep track of this with an issue.

Noticed this with PR #44, which essentially just ran clang-format but lead to a segfault in the server test. Pushing an empty commit resulted in a passing test again.

On my machine, docker build . --file Dockerfile.cmake.trusty worked fine but a conventional CMake build produces test executables that crash with segfault:

• async_grpc.client_test
• async_grpc.server_test

gdb_log_server_test.txt gdb_log_client_test.txt