Tests Configurability

I think we need to provide an easy way to read config to use in Tests. Reading environment specific and other variables in test is quite frequent and the ```ConfigLoader.java``` provides an easy way of doing this. I agree that the original way of doing this (by creating a super-type of the dropwizard config class) was convoluted. Hence, this 2nd alternate. 

This still has scope for improvement as the config file is loaded from the filesystem in each test class. This may have a slight performance hit in large test suites. Maybe we should load the file in a common class part which is a part of the atam4j library and make it available to test classes? Thoughts?