Service Watchdog give up waiting for boot to finish after 15 minutes

When we get problems during the boot (Alix "killed: out of swap space") then often /var/run/bootup does not get removed - the boot script itself is killed at some point. So Service Watcher needs some timeout where it assumes the boot should be finished, and therefore something went wrong removing /var/run/bootup.
In this case, it is good for Service Watcher to start taking action, and at least start any missing things in its list.

Note: This needs a new pfsense-utils.inc that has get_uptime_sec() - see pull request in pfSense repo.

Otherwise it needs to be re-engineered to calculate uptime itself.