Reload instead of restart haproxy

Since haproxy needs to be alive for the entirety of a client session,
use the reload functionality. It'll create a new process with new
settings but leave the old process in place until the existing sessions
finish up.
Ensure haproxy service gets enabled

This used to be a side effect of a handler, which is lame. So now it's
an explicit task. We want to flush handlers before the task though to
prevent the task starting the service and then the handler restarting it
immediately after.
Merge pull request #696 from blueboxgroup/reload-not-restart

Reload haproxy instead of restarting it