Add a context to config.

def add_context(
        self,
        name,
        cluster_name=None,
        user_name=None,
        namespace_name=None,
        **attrs
        ):
        """Add a context to config."""
        if self.context_exists(name):
            raise KubeConfError("context with the given name already exists.")

        contexts = self.get_contexts()
        
        # Add parameters.
        new_context = {'name': name, 'context':{}}
        
        # Add attributes
        attrs_ = new_context['context']
        if cluster_name is not None:
            attrs_['cluster'] = cluster_name
        if user_name is not None:
            attrs_['user'] = user_name
        if namespace_name is not None:
            attrs_['namespace'] = namespace_name
        attrs_.update(attrs)

        contexts.append(new_context)