Bug: wh_posix_server.elf segfaults when running wh_posix_client.elf with --test option

[AlexLanzano]

Repro steps:

1. start client like so ./Build/wh_posix_client.elf --test
2. start server like so ./Build/wh_posix_server.elf
3. See segfault

Notes:
Looks like this is caused by the transport_cb not being set when the client connection gets torn down and reconnected after the first test.
Might be a good idea to add a CI test that uses this --test flag

[JacobBarthelmeh]

I could not reproduce the segfault but the certificate paths were incorrect. Made a fix and added a CI test here (#217)

[bigbrett]

@AlexLanzano when you get a chance could you try and reproduce on main after #217 merged?