test-http-bad-server: track close condition in an object In order to make the logic more advanced, we need to unify it. To unify it, we introduce a small object that will be responsible for tracking and enforcing "premature socket close" conditions for both proxy object (socketproxy and fileobjectproxy). More logic will be moved into the object in later changesets. Differential Revision: https://phab.mercurial-scm.org/D12041

test-http-bad-server: use more readable name for variable This make the code more accessible overall. Differential Revision: https://phab.mercurial-scm.org/D12040

test-http-bad-server: align output by using `;` This is the only message using a `,` instead of `;` and that seems unintentional. I am unifying the message before unigying the code. Differential Revision: https://phab.mercurial-scm.org/D12039