Phoenix-1112: Atomically rebuild index partially when index update fails

I think its better if this block of code lived in buildPartialIndexFromTimeStamp, as it's not related to building the index. Also, would you mind adding a comment about why you're setting the index from DISABLED to INACTIVE? Is it so that incremental maintenance will start again and data rows that are updated while the partial rebuild is occurring will get added to the index (i.e. you won't miss any)?