Fixed Import-Package of clustering.

Fixed Import-Package of clustering.

This patch changed sun.reflect into optional import package, since sun.*
packages are not guaranteed to work on all Java-compatible platforms.
http://www.oracle.com/technetwork/java/faq-sun-packages-142232.html

Requiring the sun.reflect caused failures of SingleFeatureTest of NIC
project. To pass the test, the sun.reflect package needed to be optional
import package.

Change-Id: I660da18f8ec99b98892dca61c8a9a0cc4f1ec3ae
Signed-off-by: Hideyuki Tai <Hideyuki.Tai@necam.com>