Change the way custom monitor IP/port is implemented in AS3/Big-IP

[m-kratochvil]

I want to see if we can change the way we implement the "custom monitor IP" and "custom monitor port" options for members. The way we do it now is, in my opinion, not ideal.

Currently, we apply the custom monitor IP/port to the member. On the AS3/Big-IP level this creates a separate monitor object for each member (sometimes large amount of monitors is created). On the AS3/Big-IP level, the option for custom monitor IP/port is also available on the pool-based monitor, which covers all the members in that respective pool. Hence, on the AS3/Big-IP level, I'd like to apply the custom monitor IP/port to the pool-based monitor. This of course implies that all members in the pool use the same custom monitor IP/port but every Octavia loadbalancing setup with custom monitor IP/port does exactly that.

Ideally, for example in Elektra, the option to specify the custom monitor IP and/or port would move from the member configuration, to the pool-based monitor configuration. In the CLI, I realize this would be more challenging, but hopefully doable.

I tested this proposed method via AS3, it works like a charm, and would also mitigate the issues in #226 and in #239.

This would be in my opinion more efficient, require less configuration objects on the Big-IP, saving some resources, lowering risk for issues like above. I do realize we would likely lose the flexibility for edge cases when customers would like to have various different custom monitor ports for the members within one pool.