Install a NApp.

        Raises:
            KytosException: If a NApp hasn't been found.

def install_napp(cls, mgr):
        """Install a NApp.

        Raises:
            KytosException: If a NApp hasn't been found.

        """
        try:
            LOG.info('    Searching local NApp...')
            mgr.install_local()
            LOG.info('    Found and installed.')
        except FileNotFoundError:
            LOG.info('    Not found. Downloading from NApps Server...')
            try:
                mgr.install_remote()
                LOG.info('    Downloaded and installed.')
                return
            except HTTPError as exception:
                if exception.code == 404:
                    LOG.error('    NApp not found.')
                else:
                    LOG.error('    NApps Server error: %s', exception)
            except URLError as exception:
                LOG.error('    NApps Server error: %s', str(exception.reason))
            raise KytosException("NApp not found.")