Fix job control in console for Panda and Penguin

[ddermendzhiev]

This PR does two things, fixing Job Control in two scenarios.

1. Scenario: you run Panda with two serial devices, exposing the second over telnet. Problem: Job Control was not working because the curproc was the session (process group) leader, thus not allowing setsid() to create a new session (setsid() man page). Solution: fork() before calling setsid()
2. Scenario: you run Penguin and connect to the shell exposed over telnet. Problem: Ctrl+C was not working as expected. The character gets rendered in the output, but no SIGINT is raised. Solution: explicitly re-raise the proper signal with its default handler (SIG_DFL)