Added handler for requests.exceptions.ConnectionError to discogs plugin.

Added handlers for ConnectionError in 2 places.  It should cover these exceptions when encountered in the discogs plugin.  The exception is not handled directly in the get_albums() function but handled in the candidates() function which calls it as that is where the possible DiscogsAPIError was being handled.  It is also requires less code to be modified.  Tested on a large import and this fix does enable the import to complete and outputs the error message properly.