Automatically restart qubesd when it crashes

qubesd service is critical for Qubes usage, so even in case of critical
error crashing the whole service, make sure it is restarted.
Set delay to 1s (default 100ms), to allow other services to restart too,
if crash was caused by some other service (like libvirtd crash).

QubesOS/qubes-issues#2960

linux/systemd/qubesd.service

@@ -6,6 +6,8 @@ Type=notify
 ExecStart=/usr/bin/qubesd
 StandardOutput=syslog
 KillMode=process
+Restart=on-failure
+RestartSec=1s
 
 [Install]
 WantedBy=multi-user.target