Restore exception chaining in test_context

When we did the linting changes, these exceptions were changed to raise ... from None. This removed the default exception chaining. We want the chaining here to better report startup errors, so do it explicitly.

Reduce the time we wait for get_server_port_via_pid so that it is less than the time we wait for pre_init to report the port. This way we can see the exception from get_server_port_via_pid instead of just a generic port not available error.

Related: !991 (merged)