[N1QL] advise could give an create statement with an index name that already exists

repro:
1.enable dp
2.load travel-sample
3.create an index CREATE INDEX adv_sourceairport_airlineid ON `travel-sample`(fake)
4.run advise for this statement
advise SELECT * FROM `travel-sample` r JOIN `travel-sample` a ON r.airlineid = META(a).id WHERE r.sourceairport = "SFO"

advise statement will STILL give you this output

"recommended_indexes": {
"indexes": [
{
"index_statement": "CREATE INDEX adv_airlineid_sourceairport ON `travel-sample`(`airlineid`,`sourceairport`)",

^ above create index statement would not work if copy and pasted because that index name already exists in your index list