fix(peering_test) : Fix the peering_test to check the connection explicitly added

[TakashiMatsuda]

Overview

This PR is intended to correct the test for peering.PeeringService.

Detail

The current master code tests that h1 is connected to h2 on L69.
I have modified it to check h3.
This test appeared to be intended to test that host.Connect is working correctly after the PeeringService has been started.

Processing flow in the modified area

// h1 is now connected to h2 and h4
h1 -> [h2, h4]
// then explicitly connect to h3 
h1 -> [h2, h4, h3]
// now we want to test is h3
h1 -> h3

Comment

This is the first time I'm commiting to this repository. Please point it out if this PR breaks any conventions.
I've read and respect CONTRIBUTING.md and CONTRIBUTING_GO. Thank you.

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❤️

Fixing tests is always welcome! Thanks!