Don't run VTN Coordinator test that may fail under heavy load.

Some VTN Coordinator tests may fail if the build host is under heavy load,
especially tests that require accuracy of system timer.
This patch eliminates those tests.

Change-Id: I9bc76e7256799a415003a00698e8d9c275d7f7d6
Signed-off-by: Shigeru Yasuda <s-yasuda@da.jp.nec.com>