Update VTN Coordinator sources to the latest version.

VTN Coordinator version is changed to 6.0.0.0-SNAPSHOT.

Change-Id: I598d1d1145de4fe7a5826f1619b4a0560ad4ef0f
Signed-off-by: Shigeru Yasuda <s-yasuda@da.jp.nec.com>
Merge "Update VTN Coordinator sources to the latest version."