Fuzz the peerset manager to test coherency

[tomaka]

Write a test for the peerset crate that uses the API in a random way, and verifies if the output is coherent (eg. if the peerset doesn't send "dropped" twice in a row for the same node).

cc @debris

[tomaka]

List of things to verify in the output:

• "Connect" must only be emitted for a node for which the latest emitted message is a "Drop" or a "Reject", or if the test called dropped for this node.
• "Drop" must only be emitted for a node for which the latest emitted message is a "Connect" or an "Accept".
• "Accept" or "Reject" must not be emitted about a node for which the latest emitted message is a "Connect".

Please note that the point of the test is not just to be a basic usage, but to try the weirdest situations imaginable.

[gterzian]

Ok I'll take this on...

[tomaka]

Triage: this is done.