[frontend] map build status 1000 to 'unknown' string
    
    For some reason, the alembic upgrade did not update
    status_to_order/order_to_status PostgreSQL functions for me.
    Then, when I forked some project, some builds had status "forked
    == 8) -- and the manual query from get_copr_builds_list() returned
    status=1000; because we did not map 1000 to concrete string, magic
    error (shown in httpd error_log only) broke the jinja rendering
    and it led to hard time with debugging (let's ease the debugging).