Speed up tests accessing User.password

Decrease User.settings.saltWorkFactor in order to speed up unit-tests.
Merge pull request #135 from strongloop/feature/speed-up-user-passwords

Speed up tests accessing User.password
Refactor method processAppConfig() from app.boot()
Implement app option loggerFormat

The new option is used by app.installMiddleware to configure
the log format used by loopback.logger middleware.