Fix total_shards_per_node config

Before this was only being applied after the index was created.  Now it
gets a special value if the index is being reindexed to spread the index
as evenly as possible during the write traffic reindex event.  Once the
reindex is done the value is set to whatever the user configured it to
be.

Change-Id: I9807023baa2fa8c4e4a5a79cf38d1c372462ddfb
Merge "Fix total_shards_per_node config"