Add a test in core to raise an error when we have a difference in the expected jar version and what version is currently loaded.

Logstash has a patch to silence theses warning but as suggested by @jordansissel We should have a test for them to be more proactive about our jars constraints.

```
--- jar coordinate com.fasterxml.jackson.core:jackson-databind already loaded with version 2.7.4 - omit version 2.7.3
--- jar coordinate com.fasterxml.jackson.core:jackson-core already loaded with version 2.7.4 - omit version 2.7.3
--- jar coordinate com.fasterxml.jackson.core:jackson-databind already loaded with version 2.7.4 - omit version 2.7.3
--- jar coordinate com.fasterxml.jackson.core:jackson-annotations already loaded with version 2.7.3 - omit version 2.7.0
--- jar coordinate com.fasterxml.jackson.core:jackson-core already loaded with version 2.7.4 - omit version 2.7.3
```