Like check_own_socket_thread, we can move the functionality of monitoring parent and homedir into a thread (from handle_tick).
By doing so, it will be:

• possible: change the interval value at compile time independent to TIMERTICK_INTERVAL
• improvement: the need for check (thus, the need to spawn the thread) can be determined once
• possible: handle_tick can be removed and agent_cache_housekeeping can be improved to support exact timeout