Bug 1151: Fix for VTN Coordinator UT failure.

  * Enlarge buffer to store absolute file path.

Change-Id: I16cfa80de944618a9237d249a0506c63c4f42921
Signed-off-by: Shigeru Yasuda <s-yasuda@da.jp.nec.com>
(cherry picked from commit e24e4cb8fd736d4b601dd86e9989bb7fcddc6ec7)