Disable the packager plugin when integration tests are disabled (running a release)

Currently, when using the release scripts, the integration-tests maven profile is activated in order to enable *-tests modules, mostly so that they are loaded by maven and their versions get bumped and that their artifacts (poms/jars) get published.

However, the side-effect is that the integration-tests profile also runs the packager plugin for each *-tests module, thus creating, starting and initializing countless XWiki instances that are never used and discarded immediately (since tests are disabled).

A solution suggested by tmortagne is to disable the packager plugin when the tests are disabled, thus avoiding the problem of the XWiki instance completely and resulting in faster builds, with less I/O operations.