Optimize in place reindexing.

1.  Turn replicas on _after_ building the new index.
2.  Optimize the index before adding the replicas.  Might help some with
speed but helps more with query performance on closed indexes.
3.  Build the index in multiple processes.  Default to doing this on
linux and not on Windows.
4.  Use the 'create' action instead of the 'index' action.

Bug: 54918
Change-Id: I51101191a9e1daac794d027af23bbf6a0fb096ab
Merge "Optimize in place reindexing."