Create a PoC of OptaShift REST API tests

The OptaShift Employee Rostering app provides several REST API endpoints, currently without any test coverage. Aim of this ticket is to create a PoC of such tests and make them runnable on Wildfly 11.

Currently, there is an example of REST API tests in the app. Arquillian is used for the test setup, which might not be the right tool for this purpose.

The goals of this ticket are:

• setup tests using maven Cargo plugin
• refactor and complete existing tests of Skill endpoint
• remove configuration connected with Arquillian