TODOS: -------- * Add --socket option if no HOME found (sessiond) * Use realloc() in ask_sessiond() (liblttngctl) * perror() --> PERROR() (everywhere in the code) * Add a command to "lttng" to consume data when the tracer is in flightrecorder mode * Fix error handling for UST support when enabling events on all applications. * Support for UST remaining domains (PID, EXEC_NAME, FOLLOW_CHILDREN).