Return a timedelta that Koji considers to be average for this package.

        Calls "getAverageBuildDuration" XML-RPC.

        :param package: ``str``, for example "ceph"
        :returns: deferred that when fired returns a datetime object for the
                  estimated duration, or None if we could find no estimate for
                  this package.

def getAverageBuildDuration(self, package, **kwargs):
        """
        Return a timedelta that Koji considers to be average for this package.

        Calls "getAverageBuildDuration" XML-RPC.

        :param package: ``str``, for example "ceph"
        :returns: deferred that when fired returns a datetime object for the
                  estimated duration, or None if we could find no estimate for
                  this package.
        """
        seconds = yield self.call('getAverageBuildDuration', package, **kwargs)
        if seconds is None:
            defer.returnValue(None)
        defer.returnValue(timedelta(seconds=seconds))