test-http-bad-server: factor code dealing with "write" in the new object This will make sure both `sendall` and `write` do the same processing and make it simpler to update that processing in the future. Differential Revision: https://phab.mercurial-scm.org/D12043

test-http-bad-server: unify log printing for `sendall` and `write` The `write` function was logging before calling the function while the `sendall` function were logging after calling the function. We align the `write` behavior on the `sendall` behavior before unifying the code. Differential Revision: https://phab.mercurial-scm.org/D12042

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