tests: fix stopping race in http client harness

[algorandskiy]

Summary

Fix for p2p-related failures as seen in this build

There is a race in libp2phttp.go

	select {
	case <-h.httpTransport.closeListeners:
	case err = <-errCh:
		expectedErrCount--
	}

h.httpTransport.closeListeners is closd in httphost.Close() and errCh gets it error from Serve loop.
Because notifyAll is now async, host.Close() finishes somitimes faster so that errCh gets a chance to be ready before h.httpTransport.closeListeners

The fix is very the same as WebsocketNetwork.httpdThread - is to handle http.ErrServerClosed explicitly

Test Plan

This is a test fix

[codecov]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.68%. Comparing base (791c5ae) to head (b8f7fa7).
⚠️ Report is 3 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
network/p2p/testing/httpNode.go	0.00%	2 Missing ⚠️
network/p2pNetwork.go	0.00%	0 Missing and 2 partials ⚠️

❗ There is a different number of reports uploaded between BASE (791c5ae) and HEAD (b8f7fa7). Click for more details.

HEAD has 4 uploads less than BASE

Flag	BASE (791c5ae)	HEAD (b8f7fa7)
full_coverage	4	0

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #6566       +/-   ##
===========================================
- Coverage   63.66%   47.68%   -15.99%     
===========================================
  Files         484      645      +161     
  Lines       67688    87972    +20284     
===========================================
- Hits        43095    41946     -1149     
- Misses      21077    43264    +22187     
+ Partials     3516     2762      -754     

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