i18n - fixing regression in gettext packaging for cli

Our katello-cli was missing all MO files. This was due to %find_lang macro without file list used in %files.

I have fixed that. Also, I moved our pofilter check into Makefile and rewritten it so it can leverage full power of GNU Make on multicore systems, because this check was a little bit slow. On my system:

    # make check
    real 0m8.613s
    user 0m7.577s
    sys 0m0.627s

Now with my patch (assuming 4 core box):

    # make check -j4
    real 0m4.202s
    user 0m12.715s
    sys 0m0.850s

I am going to do this improvement also on katello and katello-disconnected.