Update index creation before upgrading to Mongo 4.2

[MrCreosote]

Mongo 4.2 change how indexes are built and it appears as though the default behavior is background creation. It's not clear if the client blocks while the index is created. If not, the service could start while the necessary indexes aren't in place which could cause corrupt data and index build fails.

[MrCreosote]

It seems that now the indexes will allow writes while they're building, which means the unique constraint can be violated:
https://www.mongodb.com/community/forums/t/block-until-index-is-created/228390

As such, the index build will need to be updated to

• createIndex for all the indexes
• wait for some period of time (1s?)
  • This allows the indexes to be created on a fresh install
• check that all the indexes are correctly created, and throw an error telling the user to create the missing indexes if not.
• The alternative is to sit there and poll until the indexes are built, but that seems like a waste of time - better to just shut down.