The NMClient seems to always emit an extra notify::primary-connection
signal on startup which resulted in always calling connectivityChanged
and so reloading the accounts in the daemon for no reason.

We save the NMActiveConnection pointer to make sure it has really changed.

Change-Id: I8ee920c0f12e0e599bde37a2a0adf2a36561a75b
Tuleap: #1097