Even if update check fails for some reason (network problem, apt-get lock
being held etc), don't mark the service as failed. The update check
mechanism is designed this way to not worry about such single failures
- other VM(s) may still check and report updates availability.
FixesQubesOS/qubes-issues#1889
Among other things this also fixes build failure - those scripts were
installed but not listed in spec file.
Actual check doesn't perform 'apt-get update', so do that when running
"standalone" (not as a hook from 'apt-get').
QubesOS/qubes-issues#1066
