Fix a random unit test failure at usage aggregator
Fix a random unit test failure at usage aggregator

Accumulated usage are received by usage aggregator in a random order.
To order the accumulated usage submission, use transform.reduce.

Fixes github issue #64.

KRuelY/cf-abacus,BetaFood/cf-abacus-dev,KRuelY/cf-abacus,kurumai/cf-abacus,18F/cf-abacus,BetaFood/cf-abacus-dev,jsdelfino/cf-abacus-experiment,jsdelfino/d-abacus,jsdelfino/cf-abacus-experiment,sasrin/cf-abacus,jsdelfino/d-abacus,jsdelfino/d-abacus,kurumai/cf-abacus,18F/cf-abacus,cloudfoundry-incubator/cf-abacus,jsdelfino/x-abacus,cloudfoundry-incubator/cf-abacus,sasrin/cf-abacus,jsdelfino/d-abacus,jsdelfino/cf-abacus-experiment,pombredanne/cf-abacus,rajkiranrbala/cf-abacus,nmaslarski/cf-abacus,danparsons/cf-abacus,rajkiranrbala/cf-abacus,BetaFood/cf-abacus-dev,rajkiranrbala/cf-abacus,jsdelfino/x-abacus,nmaslarski/cf-abacus,pombredanne/cf-abacus,jsdelfino/x-abacus,rajkiranrbala/cf-abacus,KRuelY/cf-abacus,18F/cf-abacus,jsdelfino/x-abacus,nmaslarski/cf-abacus,cloudfoundry-incubator/cf-abacus,nmaslarski/cf-abacus,KRuelY/cf-abacus,danparsons/cf-abacus,danparsons/cf-abacus,pombredanne/cf-abacus,sasrin/cf-abacus,pombredanne/cf-abacus