fix(sockets): return right headers for request upgrade

[Threated]

Supersedes #210

According to the spec we should return the protocol we decided on which I just called tcp and enforced the name everywhere because we don't want the client to decided as httpd for example only permits upgrades of names that it knows about:

<VirtualHost *:80>
    ProxyPass / http://broker:8080/ upgrade=tcp
    ProxyPassReverse / http://broker:8080/
</VirtualHost>

Also I improved the test a so that it works even if we run a lot of them in parallel

[Threated]

I cherry picked my flaky tests fix from the other branch. At least one useful commit from there 😭