discover/grub2: Allow to separate the --id argument using a space char

[petitboot] / test / urls / data / join-full.test

http://hostname.tld:80/path1/file1 https://otherhost.tld:81/path2/file2
scheme  https
host    otherhost.tld
port    81
path    /path2/file2
dir     /path2/
file    file2