JCLOUDS-457: Using assertj assertions

testng assertions have been replaced with assertj
assertions.
Extracting is an interesting new feature in assertj 1.5.0, almost like they hacked on part of Java 8 lambdas:

https://github.com/joel-costigliola/assertj-core/wiki/New-and-noteworthy#assertj-core-1.5.0