OPENDJ-842 On Windows, the setup command hangs when the length of the install path is too long

Code review: csovant

Jars now appear only once in the classpath (they were appearing twice).
INSTALL_ROOT and INSTANCE_ROOT represented the same absolute paths despite having different relative paths, resulting in the jars appended twice to the classpath.
After this change, the paths are using the absolute paths instead of the relative paths.

_script-util.bat:
Fixed jars appearing twice in the classpath