Tests: update tests for the current API

It also fixes many code indentation issues so I really recommend to
review changes with '--ignore-all-space' equivalent.
Tests: code polishing - use normalized signal signatures
QOfonoNetworkOperator: Remove recently added value semantics

Introduced with 856f137 ([libqofono] add auto tests.) in order to make
tests build possible. Hopefully nobody used it elsewhere and so it is
safe to simply remove it.
Fix memory leaks with QDBusPendingCallWatcher

This also refactorizes proper code to follow the same pattern of calling
watcher->deleteLater() at the very start of the callback (also good with
respect to callbacks with more than one return statement.)

[libqofono] Fix memory leaks on DBus calls