Update Omnibus config with sane defaults
Update Omnibus config with sane defaults

* Use S3 caching
* Enable build retries
* Bump fetcher timeout

chef/supermarket,tas50/supermarket,chef/supermarket,robbkidd/supermarket,chef/omnibus-supermarket,nellshamrell/supermarket,chef/supermarket,chef/supermarket,juliandunn/supermarket,robbkidd/omnibus-supermarket,chef/supermarket,robbkidd/supermarket,juliandunn/supermarket,tas50/supermarket,robbkidd/supermarket,tas50/supermarket,fhanson/omnibus-supermarket,juliandunn/supermarket,nellshamrell/supermarket,fhanson/omnibus-supermarket,nellshamrell/supermarket,robbkidd/omnibus-supermarket,chef/omnibus-supermarket,robbkidd/supermarket,chef/omnibus-supermarket,nellshamrell/supermarket,juliandunn/supermarket,fhanson/omnibus-supermarket,tas50/supermarket,robbkidd/omnibus-supermarket