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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def validate_rmq_cluster_running_nodes(self, sentry_units):
 """Check that all rmq unit hostnames are represented in the cluster_status output of all units. :param host_names: dict of juju unit names to host names :param units: list of sentry unit pointers (all rmq units) :returns: None if successful, otherwise return error message """

        host_names = self.get_unit_hostnames(sentry_units)
        errors = []

        # Query every unit for cluster_status running nodes
        for query_unit in sentry_units:
            query_unit_name = query_unit.info['unit_name']
            running_nodes = self.get_rmq_cluster_running_nodes(query_unit)

            # Confirm that every unit is represented in the queried unit's
            # cluster_status running nodes output.
            for validate_unit in sentry_units:
                val_host_name = host_names[validate_unit.info['unit_name']]
                val_node_name = 'rabbit@{}'.format(val_host_name)

                if val_node_name not in running_nodes:
                    errors.append('Cluster member check failed on {}: {} not '
                                  'in {}\n'.format(query_unit_name,
                                                   val_node_name,
                                                   running_nodes))
        if errors:
            return ''.join(errors)