Make keepalived.tmpl customizable

[stephenmoloney]

Issue:

If something in keepalived.tmpl does not work for any reason on your cluster, then your out of luck as the docker image has crystallized it.

Suggestion:

Optionally allow for the addition of a customized keepalived.tmpl, possibly through a configmap - Not sure how go code works in terms of compilation, etc but would that work - not sure.

[ms4720]

see #67