Use fake reply in EnginioModel::remove and EnginioModel::setProperty.

It unifies behavior between EnginioModel and EnginioClient
Add more QVERIFY in EnginioClient tests
Do not return null EnginioReply in EnginioModel::setProperty.

Create a proper reply when an user try to update unknown role.
Make test check only one thing

EnginioModel is allowed to make additional requests so the test should
query only requests that were created by it.
Move re-parenting of a QNetworkReply instance to the EnginioReply ctor.

EnginioReply should take ownership of QNetworkReply, so there is no need
for manual re-parenting.
Merge pull request #146 from nierob/smallFixes

Small fixes