Add missing requirements packages

Change-Id: Icd7a64cda4170802d35e437f8b68507daddc3f31
diff --git a/requirements.txt b/requirements.txt
index cf35ea1..0cf6122 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -11,3 +11,4 @@
 # replace when we can use upstream (needs python 3.6)
 git+https://github.com/zdw/robotframework-importresource@b81b87aabaee0594e966687b41e3674b866f28ee
 cord-robot==2.1.1
+virtualenv