Test suite: also include the content of /var/log/tor/log in $scenario.tor when...

Test suite: also include the content of /var/log/tor/log in $scenario.tor when tor failed to bootstrap (refs: #16793)

cd0d5139 says it will do this: "When Tor fails
to bootstrap, save Tor logs". But it only saves bits of the Journal, i.e.
the initial logs sent by tor to syslog before our Log notice file
/var/log/tor/log is taken into
account (commit:41951755). So the resulting
$scenario.tor file contains very little info, and typically not the info we need
to debug stuff. Let's fix that.