tests: support setting random seed

Log the random seed used when running tests and provide means to re-use
it in a later run.

Type: feature

Change-Id: I18d2a36ee802b901d4cca5577df41cec07f09cc0
Signed-off-by: Klement Sekera <ksekera@cisco.com>
diff --git a/test/Makefile b/test/Makefile
index 7ec8d4a..3a78a3f 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -341,6 +341,8 @@
 	@echo ""
 	@echo " SOCKET=1             - Communicate with VPP over Unix domain socket instead of SHM"
 	@echo ""
+	@echo " RND_SEED=seed        - Seed RND with given seed"
+	@echo ""
 	@echo "Creating test documentation"
 	@echo " test-doc            - generate documentation for test framework"
 	@echo " test-wipe-doc       - wipe documentation for test framework"