[Bluetooth] stopDiscovery API fix

Return an error message to javascript when there is no discovering
when user requests to stop it.
[Bluetooth] setChangeListener API fix

Now 'AdapterUpdated' JSON message is sent to javascript and
checks listener existence before calling its callbacks.
Merge pull request #344 from eurogiciel-oss/fix_setChangeListener

Fix set change listener
Merge pull request #345 from eurogiciel-oss/stopDiscovery

[Bluetooth] stopDiscovery API fix