auto-t: iwd.py: add roam() method

This will use the Roam() developer method to force a roam to
a certain BSS. This is particularly useful for any test requiring
roams that are not testing IWD's BSS selection logic. Rather than
creating hwsim rules, setting low RSSI values, and waiting for the
roam logic/scan to happen Roam() can be used to force the roam
logic immediately.

autotests/util/iwd.py

@@ -542,6 +542,12 @@ class Device(IWDDBusAbstract):
                                                 IWD_STATION_DEBUG_INTERFACE)
         self._station_debug_if.ConnectBssid(dbus.ByteArray.fromhex(address.replace(':', '')))
 
+    def roam(self, address):
+        self._station_debug_if = dbus.Interface(self._bus.get_object(IWD_SERVICE,
+                                                self.device_path),
+                                                IWD_STATION_DEBUG_INTERFACE)
+        self._station_debug_if.Roam(dbus.ByteArray.fromhex(address.replace(':', '')))
+
     def __str__(self, prefix = ''):
         return prefix + 'Device: ' + self.device_path + '\n'\
                + prefix + '\tName:\t\t' + self.name + '\n'\