add ability to select which columns to list

[bsdci]

add ability to select which columns to list

[igalic]

relatedly, from IRC:

<gronke> I want list json output :D
<meena> --libxo=
<meena> please, add that to the issue i opened.
<meena> i dunno how i forgot about that ~_~
<meena> hrm… there's no libxo for python ☹
<meena> so, does that mean we need someone to write a cython wrapper?

[gronke]

https://github.com/iocage/libiocage/blob/6068a5c4ec7c4c2e7fdacaad8740e7f2d27cc3e3/libiocage/cli/list.py#L52

[igalic]

haah! thanks 😀