Added new unit tests

Added new unit tests to GraphMLConverter class.
Fixed the Sonar issue.

Issue-ID: SDC-2327
Signed-off-by: Krystian Kedron <k.kedron@partner.samsung.com>
Change-Id: I985a860012c0c2b0b6524c0a2346415cb113d83c
diff --git a/asdctool/src/test/resources/config/janusgraph.properties b/asdctool/src/test/resources/config/janusgraph.properties
new file mode 100644
index 0000000..4f8d3ad
--- /dev/null
+++ b/asdctool/src/test/resources/config/janusgraph.properties
@@ -0,0 +1 @@
+storage.backend=inmemory