CBAS : User with analytics_reader role is able to create/drop secondary indexes

Build : 5.0.0-758

A user with analytics_reader role is able to create/drop secondary indexes.

Steps to reproduce :
1. Load beer-sample bucket in CB
2. Create 2 users - analytics_manager and analytics_reader. analytics_manager user should have analytics_manage and bucket_admin roles for atleast beer-sample bucket. analytics_reader user should have analytics_reader role.
3. Create analytics bucket beers and beers_ds dataset.
4. As user analytics_reader, try to create a secondary index : create index idx1 on beer_ds(city:string). The index gets created. Similarly, analytics_reader user is also able to drop a secondary index.