Eliminate blocking D-Bus calls in QOfonoManager

QOfonoManager constructor was actually making two blocking calls - first org.ofono.Manager.GetModems and then org.ofono.Modem.GetProperties (per each modem but we only have one). The latter was totally unnecessary because GetModems returns all the modem properties, there's no need to query them again.
What about error path processing? E.g. just logging