Construct TestSuite.module_list much more efficiently
    
    So this used to get constructed by literally running 'dnf module
    list' and then parsing the output. Then it got re-written
    to use the dnf library to quite laboriously construct a thing
    which looked a lot *like* the output of 'dnf module list' only
    without some awkward-to-parse bits, and run *that* through the
    existing parser to get the dict-of-lists-of-dicts that we
    ultimately want.
    
    Take a step back and that is rather silly, though. We're doing
    a bunch of fragile string concatenation to produce a whole
    intermediate format we don't really need and then doing fragile
    string parsing on that to produce the thing we *do* want. Let's
    just cut out the middleman and have `module_list` build itself
    directly from the info we get from the dnf library. This makes
    the whole thing smaller, more robust and 100% less reliant on
    string parsing...
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>