add notify script via environment variable

[muhlba91]

keepalived supports executing notify scripts on events, which come in handy when having to react to events, e.g. when performing a failover, and trigger any update. In this specific case it is needed for Hetzner Failover/Floating IPs to perform a JSON API call to the Hetzner API and notify them about the changed IP assignment.

As mentioned in a comment in @cornelius-keller's PR kubernetes-retired/contrib#2912, this repository here is more maintained and, therefore, I have applied the necessary changes and hopefully this can get merged. :)

[CLAassistant]

All committers have signed the CLA.

[coveralls]

Coverage decreased (-0.08%) to 15.014% when pulling 2b0183e on muhlba91:notify_script into f3b9e29 on aledbf:master.

[aledbf]

@muhlba91 please sign the CLA

[muhlba91]

@aledbf thanks for you rresponse. :) I have signed the CLA now.

[aledbf]

@muhlba91 thanks!

[muhlba91]

@aledbf cool, thanks for merging! :)
btw, when can we expect a new release containing this feature?

[cornelius-keller]

thanks @muhlba91 @aledbf , I am happy that this is merged finally somewhere else than in my private for!

[aledbf]

@muhlba91 now :) https://github.com/aledbf/kube-keepalived-vip/releases/tag/0.32