v0.15.5

Features:
* Add an exclusive lock for nmstate  handler instances (#487) (#490)
* Adapt to external k8s (#465)
* [release-0.15] Add node ready state probe (#481)
* [release-0.15] Annotate tests with polarion IDs (#453)

Bugs:
* Ensure probes are run after success nmstatectl rollback (#485)
* test: Don't use 'sleep 5' at vlan-filtering script (#479)
* Stabilize 0.15 tests (#472)
* Pin nmstate to 0.1 (#463)

```
docker pull HANDLER_IMAGE
```
