Bump os-ken from 3.1.0 to 4.1.0

Bumps [os-ken](http://www.openstack.org/) from 3.1.0 to 4.1.0.

---
updated-dependencies:
- dependency-name: os-ken
  dependency-version: 4.1.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -5,6 +5,6 @@ networkx>=1.9
 pbr>=1.9
 prometheus_client==0.23.1
 ruamel.yaml==0.18.16
-os_ken==3.1.0
+os_ken==4.1.0
 beka==0.4.2
 pytricia>=1.0.0