turris-maintain: maintain-reboot fails because of unexpected UCI

The solution is most likely to use EUCI instead of plain UCI to handle correctly lists.

In general all scripts in turris-maintain should be refactored as I looked at them.

At the moment this issue makes it so reboot from Foris does not work when IP address on wan is saved as list and not as option.

Oct 20 12:45:14 turris foris-controller[7712]: Traceback (most recent call
last):


Oct 20 12:45:14 turris foris-controller[7712]: File
"/usr/bin/maintain-reboot", line 58, in <module>


Oct 20 12:45:14 turris foris-controller[7712]: ips += [e for e in
uci_get("network", "wan", "ip6addr", "").split(" ") if e]


Oct 20 12:45:14 turris foris-controller[7712]: AttributeError: 'tuple'
object has no attribute 'split'