Listen to right post-npm i hook in generator tests.

The generator tests have been broken thanks to a bit of race condition. Our tests were waiting for yeoman to emit a `kraken:app:installDependencies` but this event fires at the beginning of an npm install, not at the end.

Changes to listen to `npmInstall:end` works since that event fires at the right tim.

This realized a new error on our tests but it's a result of mocha presently being broken.

`this.timeout(0)` acts differently as of 1.21.0. This has been been resolved in master but has not yet been pushed. To account for this, currently pegging mocha to `~1.20`.