**Summary** of the plot of the `discover_peer_after_disconnect` test:

1. `swarm2` connects to `swarm1`.
2. `swarm2` requests an identify response from `swarm1`.
3. `swarm1` sends the response to `swarm2`.
4. `swarm2` disconnects from `swarm1`.
5. `swarm2` tries to disconnect.

**Problem**

`libp2p-identify` sets `KeepAlive::No` when it identified the remote. Thus `swarm1` might
identify` `swarm2` before `swarm2` identified `swarm1`. `swarm1` then sets `KeepAlive::No` and thus closes the
connection to `swarm2` before `swarm2` identified `swarm1`. In such case the unit test
`discover_peer_after_disconnect hangs indefinitely.

**Solution**

Add an initial delay to `swarm1` requesting an identification from `swarm2`, thus ensuring `swarm2`
is always able to identify `swarm1`.