Fix CREATE INDEX behavior when keyspace and field names are the same

From Sitaram:

create index ix5 on default(default.f1);

cbq> explain select f1 from default d where d.f1 = 5;
{
"requestID": "5629cfe1-c7e3-4dda-bb3d-502765c929d2",
"errors": [

{ "code": 4000, "msg": "No primary index on keyspace default. Use CREATE PRIMARY INDEX to create one." }

],
}