[rpmbuild] nicer live logs
    
    - custom method uses GentlyTimeoutedPopen
        - it doesn't buffer std{out,err} outputs as run_cmd() does
        - it is wise to have some timeout (for now 3600s)
    - print all the debugging commands pipes.quote()'d
    - the _overall_ live log for source methods is now processed
      through "sed && tee" pair instead of additional logger handler
      (as was done before in mock.py only)
    - dump the executed command directly by GentlyTimeoutedPopen