pytest: Test the new peer_connected hook with a reject plugin

This plugin just rejects `node_id`s it gets told about.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

tests/plugins/reject.py

@@ -0,0 +1,38 @@
+#!/usr/bin/env python3
+"""Simple plugin to test the connected_hook.
+
+It can mark some node_ids as rejects and it'll check for each
+connection if it should be disconnected immediately or if it can
+continue.
+
+"""
+
+from lightning import Plugin
+
+plugin = Plugin()
+
+
+@plugin.hook('peer_connected')
+def on_connected(peer, plugin):
+    if peer['id'] in plugin.reject_ids:
+        print("{} is in reject list, disconnecting".format(peer['id']))
+        return {'result': 'disconnect'}
+
+    print("{} is allowed".format(peer['id']))
+    return {'result': 'continue'}
+
+
+@plugin.init()
+def init(configuration, options, plugin):
+    plugin.reject_ids = []
+
+
+@plugin.method('reject')
+def reject(node_id, plugin):
+    """Mark a given node_id as reject for future connections.
+    """
+    print("Rejecting connections from {}".format(node_id))
+    plugin.reject_ids.append(node_id)
+
+
+plugin.run()