jenkins: clean up .ndn dir before test

Change-Id: I37c1dfa155c6f57b69db5893ae7c722f784c2414
diff --git a/.jenkins.d/30-test.sh b/.jenkins.d/30-test.sh
index 4109bd5..7e6610e 100755
--- a/.jenkins.d/30-test.sh
+++ b/.jenkins.d/30-test.sh
@@ -2,4 +2,7 @@
 set -x
 set -e
 
+# Prepare environment
+sudo rm -Rf ~/.ndn
+
 ./build/unit-tests -l test_suite