Unable to update system to the latest rolling
```
vyos@r4-roll:~$ add system image https://downloads.vyos.io/rolling/current/amd64/vyos-rolling-latest.iso
Trying to fetch ISO file from https://downloads.vyos.io/rolling/current/amd64/vyos-rolling-latest.iso
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 309M 100 309M 0 0 13.8M 0 0:00:22 0:00:22 --:--:-- 14.8M
ISO download succeeded.
Checking SHA256 (256-bit) checksum...
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 106 100 106 0 0 190 0 --:--:-- --:--:-- --:--:-- 190
Found it. Verifying checksum...
sha256sum: 'https://downloads.vyos.io/rolling/current/amd64/vyos-rolling-latest.iso.sha256': No such file or directory
Signature check FAILED.
Installation will not be performed.
Exiting...
vyos@r4-roll:~$
```
It happened after that commit https://github.com/vyos/vyatta-cfg-system/pull/131/commits/34b46ca2738fe6a9d15b0ee52deb3d3d5f76606e
Something wrong with that code https://github.com/vyos/vyatta-cfg-system/blob/current/scripts/install/install-image#L166-L182
Log from my previus update from 26 oct:
Maybe it expect "vyos-1.3-rolling-202010260327-amd64.iso" but get vyos-rolling-latest.iso
```
root@r4-roll:/home/vyos# sha256sum --check vyos-rolling-latest.iso.sha256
sha256sum: vyos-1.3-rolling-202010260327-amd64.iso: No such file or directory
vyos-1.3-rolling-202010260327-amd64.iso: FAILED open or read
sha256sum: WARNING: 1 listed file could not be read
root@r4-roll:/home/vyos#
root@r4-roll:/home/vyos# ls
1.txt test.sh vyos-rolling-latest.iso vyos-rolling-latest.iso.sha256
root@r4-roll:/home/vyos# mv vyos-rolling-latest.iso vyos-1.3-rolling-202010260327-amd64.iso
root@r4-roll:/home/vyos# sha256sum --check vyos-rolling-latest.iso.sha256
vyos-1.3-rolling-202010260327-amd64.iso: OK
root@r4-roll:/home/vyos#
```