This prevents conversion of QByteArray to QString from truncating content at a null byte in the QByteArray. This truncation can be a problem if the response body is a binary object (e.g. PDF)
reuse the existing manager and just clear its headers and cookies.
This avoids repeatedly setting up the SIGNAL/SLOT callback stuff which
is leading to unclosed pipes on Ubuntu, eventually causing "too many
open files" errors in large test suites.