> test: warn if nodes not connected before disconnect_nodes
> test: remove redundant two-way disconnect_nodes calls
> There's no harm in calling disconnect_nodes for nodes that weren't connected (in this case it's a no-op). However, detecting this case and logging a warning can help ensure that tests are behaving as expected.
>
> In addition, since disconnect_nodes works bidirectionally, I removed all instances of this pattern:
>
> ```
> disconnect_nodes(self.nodes[0], 1)
> disconnect_nodes(self.nodes[1], 0)
> ```
This is a backport of core#18890
One of the 3 commits is a no-op for our codebase, as it is touching only a segwit related test.