Check if a conda channel is valid.

def is_valid_channel(self,
                         channel,
                         conda_url='https://conda.anaconda.org',
                         non_blocking=True):
        """Check if a conda channel is valid."""
        logger.debug(str((channel, conda_url)))
        if non_blocking:
            method = self._is_valid_channel
            return self._create_worker(method, channel, conda_url)
        else:
            return self._is_valid_channel(channel, conda_url=conda_url)