test: check server status in test-tls-psk-client
Add assertions to sequential/test-tls-psk-client to check if the spawned OpenSSL server has exited in any way except for the expected termination by the cleanUp() function. The added assertions will prevent the test from spinning forever trying to connect to the non-existent server in the case that the spawned process has exited. Include stderr and stdout in the assertion failure message to aid debugging.