s/OldNewMap/NewShardInfo/

Splitting a shard update info variable into two types, a one for one replacement scenario and a completely new map scenario.

The one_for_one requires the same number of shards, the replacement scenario doesn't.
Remove the old redis:shard update code.
Split populate_info_table in two.

Now allows you to populate any of the Read/Write map sets (old, new, current) with the old method replaced by a convenience wrapper for the current set.
Change oldnewmap to {one_for_one, OldNewMap}.
Add {replacements, NewUrls} shard update mode.
Small piece of documentation on shard updating.
Adds logplex_shard to the upgrade.
Merge branch 'v55' into v56