connection: Clear all cached objects when connection closes

For example, we didn't clear the iface list. So if a libvirtd was
restarted, the active connection is closed, but the old ifaces
which reference the closed connection hang around. Trying to launch the
addhw dialog for example doesn't work after reopening a new connection.

src/virtManager/connection.py

@@ -833,11 +833,16 @@ class vmmConnection(vmmGObject):
             return
 
         self.vmm = None
-        self.nets = {}
+        self.nodedevs = {}
+        self.netdevs = {}
+        self.mediadevs = {}
+        self.interfaces = {}
         self.pools = {}
+        self.nets = {}
         self.vms = {}
         self.activeUUIDs = []
         self.record = []
+
         self._change_state(self.STATE_DISCONNECTED)
 
     def _open_dev_conn(self, uri):