Get the list of charms that provides or requires this interface.

        @param interface The interface for the charm relation.
        @param way The type of relation, either "provides" or "requires".
        @return List of charms

def fetch_interfaces(self, interface, way):
        """Get the list of charms that provides or requires this interface.

        @param interface The interface for the charm relation.
        @param way The type of relation, either "provides" or "requires".
        @return List of charms
        """
        if not interface:
            return []
        if way == 'requires':
            request = '&requires=' + interface
        else:
            request = '&provides=' + interface
        url = (self.url + '/search?' +
               'include=charm-metadata&include=stats&include=supported-series'
               '&include=extra-info&include=bundle-unit-count'
               '&limit=1000&include=owner' + request)
        data = self._get(url)
        return data.json().values()