Add a sleep between jar modifications to make sure file timestamp
differs on Mac

Change-Id: If94e5b32d43ef64227ca132b42de92d28b17e316
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.core/+/191297
Tested-by: JDT Bot <jdt-bot@eclipse.org>
Reviewed-by: Andrey Loskutov <loskutov@gmx.de>
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.core/+/191588
Reviewed-by: Manoj Palat <manpalat@in.ibm.com>