Make all the mocha test functions available on global

Fixes a problem where the runner does not start due to undefined functions.
   
    ReferenceError: suite is not defined
    at marionette (/home/CORPUSERS/23053085/Projects/album/client/node_modules/marionette-js-runner/lib/runtime/marionette.js:50:5)
    at Object.<anonymous> (/home/CORPUSERS/23053085/Projects/base-app/smoke-tests/marionette-test.js:4:1)


Also, allows for writing test in a normal mocha fashion.