Mask files under core/store/trivial/data/ from git

Resolve ONOS-913

The directory is added to .gitignore

Change-Id: If70e4f96961bc49df6ef70f1dc5aa0d13c1fadfa
diff --git a/.gitignore b/.gitignore
index 8f725d6..d4d4e6d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,3 +11,5 @@
 *.pyc
 dependency-reduced-pom.xml
 .idea
+
+core/store/trivial/data/