Metadata store that is immediately consistent in which to store Index Definitions

We need a metadata store that is immediately consistent and indexing should move to use it in which to store indexing definitions.

Original Problem:
[GSI] Indexes can be created with duplicate index_names when one of the indexer node is in failed over state

Steps:
1. Configure cluster. Create bucket default and load the bucket with 10k items.
Sample document:

{

  "name": "pymc0",

  "age": 0,

  "index": 0,

  "body": "VTKGNKUHMP"

}

2. Create index ind_3 on default(name). It gets created on node 2.
3. Failover Node 2.
4. Create index ind_3 on default(age). It gets created on node 1.
5. Rebalance in Node 2 with full recovery.

Now there are 2 indexes with same name "ind_3" with different index definitions.
when dropping ind_3, later one gets dropped. There is no way of controlling drop behaviour in such cases.

Expectation is, indexes with duplicate index_names shouldn't be allowed to be created.

Snapshot attached.
Log Location:

https://s3.amazonaws.com/bugdb/jira/duplicate_indexes/collectinfo-2016-12-19T082442-ns_1%4010.111.170.101.zip

https://s3.amazonaws.com/bugdb/jira/duplicate_indexes/collectinfo-2016-12-19T082442-ns_1%4010.111.170.102.zip