Flakes: Setup new fake server if it has gone away

[mattlord]

Description

We've had some flakiness in the go/mysql package's unit tests, but in particular with TestTLSRequired:

--- FAIL: TestTLSRequired (3.03s)
    server_test.go:1001: 
        	Error Trace:	go/mysql/server_test.go:1001
        	Error:      	"cannot send HandshakeResponse41: write tcp 127.0.0.1:33754->127.0.0.1:27379: write: connection reset by peer\nWrite(packet) failed\nconn 3 (errno 2013) (sqlstate HY000)" does not contain "remote error: tls: bad certificate"
        	Test:       	TestTLSRequired

That test is unique in the package in that it calls Connect multiple times. So we address that in this PR by adding handling for when the listener goes away for any reason.

In working on this, I also realized that these unit tests are all leaking goroutines. Which not only impacts the other tests in this package when they are run together, but impacts all tests that are run after it. So I added leak checker usage and plugged those leaks as well.

Related Issue(s)

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[vitess-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.14%. Comparing base (e881b9f) to head (1084086).
Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17023      +/-   ##
==========================================
+ Coverage   67.04%   67.14%   +0.10%     
==========================================
  Files        1571     1571              
  Lines      251677   251846     +169     
==========================================
+ Hits       168729   169101     +372     
+ Misses      82948    82745     -203     

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[frouioui]

FYI, this PR touches the same function #17024 modifies, but in a different way. So we should be good.

[frouioui]

❤️