Returns a list for which items are namespaces in the output of
        ip netns stored in the ip_netns_file.

def get_ip_netns(self, ip_netns_file):
        """Returns a list for which items are namespaces in the output of
        ip netns stored in the ip_netns_file.
        """
        out = []
        try:
            ip_netns_out = open(ip_netns_file).read()
        except IOError:
            return out
        for line in ip_netns_out.splitlines():
            # If there's no namespaces, no need to continue
            if line.startswith("Object \"netns\" is unknown") \
               or line.isspace() \
               or line[:1].isspace():
                return out
            out.append(line.partition(' ')[0])
        return out