Use daemon log facility for journald

otherwise messages end up in /var/log/kern.log if journald forwards to
syslog.

Reference: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=799633
(cherry picked from commit fd00f0e6)

src/util/virlog.c

@@ -920,6 +920,7 @@ virLogOutputToJournald(virLogSourcePtr source,
     journalAddString(&state, "MESSAGE", rawstr);
     journalAddInt(&state, "PRIORITY",
                   virLogPrioritySyslog(priority));
+    journalAddInt(&state, "SYSLOG_FACILITY", LOG_DAEMON);
     journalAddString(&state, "LIBVIRT_SOURCE", source->name);
     if (filename)
         journalAddString(&state, "CODE_FILE", filename);