Support for a simple fmf filter in beakerlib role
    
    This adds basic support for test selection based on metadata. The
    new "filter" variable and dict key under "repositories" accepts a
    single fmf filter. Separate script "str-filter-tests" is used to
    check provided paths and filters and lists appropriate tests on
    the standard output. Manual test listing can be combined with the
    filter functionality as well.