Make the http-port option passed to keepalive configurable

[EmielBruijntjes]

Is your feature request related to a problem? Please describe.
The keepalived pods open port 8080 on the nodes. However, this can conflict with other applications that also want to use this port.

Describe the solution you'd like
A command line argument that can be passed to the openelb-manager to specify a different port. For example "--keepalived-port=8888". The keepalived docker image already supports the "--http-port" flag, so the flag can directly be forwarded to the keepalived image.