Allow retrieving the messages corresponding to a test case

[lbroudoux]

Reason/Context

As of today, we can launch contract tests with the library and get a TestResult object that provides details on global success and also success on each operation. However, we can not easily retrieve the detailed request/response pairs or event messages that were exchanged with the tested endpoint to realize additional checks or get more informations on what's wrong.

Description

We should provide some getMessagesForTestCase(testResultId, testCaseId) and getEventMessagesForTestCase(testResultId, testCaseId) utility methods to retrieve those messages.

Implementation ideas

Those methods could be set directly on MicrocksContainer and call the REST API exposed by Microcks server.