Fixes for skipping Jersey tests.

- Avoid starting Jetty plugin when tests are skipped
- Do not skip compilation of tests with -Pskip-tests or -Dskip.tests=true (unlike -Dmaven.test.skip)

Change-Id: I095a4ebd681490a7b46827a17cdac28869ea9c94
Signed-off-by: Marek Potociar <marek.potociar@oracle.com>