Show queue filtered by distro

[kpcyrd]

It's currently not easy to use rebuildctl queue ls --head if there are multiple distros in the rebuilderd instance because it's going to show the whole queue even if you only one to inspect one for a specific distro (eg. because you've been maintaining these specific workers).

$ rebuildctl queue ls --head --distro debian
error: Found argument '--distro' which wasn't expected, or isn't valid in this context

USAGE:
    rebuildctl queue ls --head

For more information try --help