you can try with table api and use the table v_plugin to get the list of active,inactive and plugins details. 

Sample Script:

 

var request = new sn_ws.RESTMessageV2();
var headers = request .getRequestHeaders();
request.setEndpoint('https://dev34768.service-now.com/api/now/table/v_plugin?sysparm_query=active%3Dactive');
request.setHttpMethod('GET');


//Eg. UserName="admin", Password="admin" for this code sample.
var user = 'admin';
var password = 'admin';


request.setBasicAuth(user,password);
request.setRequestHeader("Accept","application/json");


var response = request.execute();
gs.print(response.getBody());


gs.print(response.getHeader("X-Total-Count"));