Add grace period for internet clients for server to assume the client is still online
Add grace period for internet clients for server to assume the client is still online

(cherry picked from commit 8578f5cf3b14a564f073c40eb6ddcda32650a6e7)

uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend