scion.sh: fix IPv6 address bug in sciond-addr subcommand (#4341)

The scion.sh sciond-addr command was returning an invalid address for IPv6 setups, resulting in "too many colons address" error when used as the `--sciond` parameter of tool invocations. Fixed by wrapping the IP in brackets before appending the port.

scion.sh

@@ -55,7 +55,7 @@ cmd_sciond-addr() {
     jq -r 'to_entries |
            map(select(.key | match("'"$1"'";"i"))) |
            if length != 1 then error("No unique match for '"$1"'") else .[0] end |
-           "\(.value):30255"' gen/sciond_addresses.json
+           "[\(.value)]:30255"' gen/sciond_addresses.json
 }
 
 run_jaeger() {