No support for relative server_port overrides

[udangel-r7]

haproxy supports relative port addresses, prefixed by a "+" or "-".

If this is set the server port is determined by adding the value to the client's port. In the base service_watcher there is currently a check to verify that the override port is an integer which breaks existing configurations.

I assume nginx doesn't support a similar behaviour, would you accept a patch or should we just maintain our own version?

[jolynch]

@udangel-r7

Since backend_port_override is provided by the user I've got no problem loosening the regex in the base watcher. If you all have a fork with a patch PR it and I can merge it.