Concurrent preset crashes when tcp_port is set

[reidprichard]

When you have more than one preset set to run concurrently, and you set defaults.tcp_port but do not set tcp_port for the presets, whichever preset starts second will crash when it tries to bind to defaults.tcp_port. It could save users a few minutes of debugging to add an error message if:

1. general.allow_concurrent_presets = true
2. presets contains > 1 key
3. More than one presets key doesn't have tcp_port set