fix(components/systemd): fix non-existing service uptime checks

[gyuho]

Error: failed to get uptime for unit kubelet: parsing time "n/a" as "Mon 2006-01-02 15:04:05 MST": cannot parse "n/a" as "Mon"

e.g.,

# sudo systemctl show --property=InactiveExitTimestamp kubelet
InactiveExitTimestamp=Fri 2024-11-08 03:20:47 UTC

# sudo systemctl show --property=InactiveExitTimestamp gpud
InactiveExitTimestamp=Sat 2024-11-02 13:51:36 UTC

# sudo systemctl show --property=InactiveExitTimestamp g2
InactiveExitTimestamp=n/a

[photoszzt]

lgtm