Use QStringList::join(QChar) overload where applicable [QtNetwork]

Use QStringList::join(QChar) overload where applicable [QtNetwork]

This is an automated change performing the following replacements:
                    join\("(.)"\) -> join('\1')
  join\(QLatin1String\("(.)"\)\)  -> join(QLatin1Char('\1'))
  join\(QStringLiteral\("(.)"\)\) -> join(QLatin1Char('\1'))

Change-Id: I5b75877ba192fa1357e67fee70dff7c0475991e8
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>