lxc-init finishes the remaining processes with SIGKILL

lxc-init finishes the remaining processes with SIGKILL

If lxc-init receives a SIGALRM, a timeout, it kills all the processes
of the container with SIGKILL. That will prevent the container to be
stuck when one process ignore the SIGTERM signal.

Each time a process exits, the timeout is resetted.

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>