Possible fix flakiness tst_EnginioModel::createAndModify

It is a guess, but it may happen that the network reply is marked as
finished and QTRY_VERIFY checks the value before finished signal is
emitted.
Fix flakiness of tst_EnginioModel::append()

EnginioReply::isFinished may return true before the finished signal is
emitted. That happens almost always when finished signal is delayed.
Simplify a string expression.
Merge pull request #196 from nierob/master

Small improvements