Cirrus config updates

* Lower replicas for commonwiki's file namespace to 1 to save some space
until we work out a way to shrink it without losing redundancy.

* Turn on enwiki in secondary search aka building mode.

* Lower replicas for all enwiki namespaces to 1 to same some space until
we work out a way to shrink it without losing redundancy.

Change-Id: I17a5cc073d592fd39fcd1fa8f505c9f4aa77d88d
Merge "Cirrus config updates"