Allow extracting profiling information from pungi-gather.
    
    `pungi-gather` (the tool that underlies both the `pkgset` and `gather`
    phases) contains profiling code that will log statistics about how long
    different function calls take.  However, pungi-koji did not contain a
    way to pass the ``--profiler`` argument to enable this.
    
    This change adds a new configuration option ``gather_profiler`` which,
    when set to true, simply passes the argument to `pungi-koji`.  Hopefully
    this can help shed some light on what is happening in some of our
    longer-running composes.
    
    Signed-off-by: Ralph Bean <rbean@redhat.com>