[connectionagent] clear last connected service when something
requests a connection.

This allows the autoconnect service to be disconnected, but
also allows it to reconnect if a connection request comes from
connman.
[connectionagent] use a timer to see if we are really online.

If after 12 seconds from 'ready' state, we are not online,
send error to ui about it.
[connectionagent] bump version to 0.8.8