Swift: set default replicas to 3

Swift: set default replicas to 3

Our existing default (replicas == 1) means that no data
(or copies) is being replicated in a multi-node Swift
environment. This seems like a bad production default
setting and could easily slip by if not set.

Setting it to 3 shouldn't hurt anything and seems to follow
suit with what several production installers (based around Puppet)
actually use. If using an installation with less than 3 swift
nodes I believe swift will do its best, and still work fine.

FWIW I noticed this when testing a multi-node Puppet swift
installation and was surprised when I didn't see any *data
files getting replicated across the storage cluster.

Change-Id: I44bdfff7aae6bdf845b79ca1f8f450c22113caed