Pin boringtun image tag (#319)

* Pin boringtun image tag

Pin the image to a tag before boringtun's cli changed.
Specifically the --disable-drop-privileges flag need a boolean param.

* Fix image name

e2e/kilo-kind-userspace.yaml

@@ -136,7 +136,7 @@ spec:
           mountPath: /etc/kubernetes
           readOnly: true
       - name: boringtun
-        image: leonnicolas/boringtun:alpine
+        image: leonnicolas/boringtun:cc19859
         args:
         - --disable-drop-privileges=true
         - --foreground