Upgrade WildFly feature pack and integration tests to WildFly 15

Description

We had to disable Elasticsearch integration tests because of a bug in WF14, namely https://issues.jboss.org/browse/WFCORE-4083
Let's upgrade to WF15 and re-enable these tests ASAP.

Environment

None

Status

Assignee

Yoann Rodière

Reporter

Yoann Rodière

Labels

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Suitable for new contributors

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Pull Request

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Feedback Requested

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Components

Fix versions

Priority

Major