Move common code for extractors based in MTV services to a new base class

Removes the duplication of the thumbnail extraction code (only MTVIE needs to override it)

youtube_dl/extractor/gametrailers.py

@@ -1,13 +1,11 @@
 import re
 
-from .mtv import MTVIE, _media_xml_tag
+from .mtv import MTVServicesInfoExtractor
 
-class GametrailersIE(MTVIE):
-    """
-    Gametrailers use the same videos system as MTVIE, it just changes the feed
-    url, where the uri is and the method to get the thumbnails.
-    """
+
+class GametrailersIE(MTVServicesInfoExtractor):
     _VALID_URL = r'http://www.gametrailers.com/(?P<type>videos|reviews|full-episodes)/(?P<id>.*?)/(?P<title>.*)'
+
     _TEST = {
         u'url': u'http://www.gametrailers.com/videos/zbvr8i/mirror-s-edge-2-e3-2013--debut-trailer',
         u'file': u'70e9a5d7-cf25-4a10-9104-6f3e7342ae0d.mp4',
@@ -17,15 +15,9 @@ class GametrailersIE(MTVIE):
             u'description': u'Faith is back!  Check out the World Premiere trailer for Mirror\'s Edge 2 straight from the EA Press Conference at E3 2013!',
         },
     }
-    # Overwrite MTVIE properties we don't want
-    _TESTS = []
 
     _FEED_URL = 'http://www.gametrailers.com/feeds/mrss'
 
-    def _get_thumbnail_url(self, uri, itemdoc):
-        search_path = '%s/%s' % (_media_xml_tag('group'), _media_xml_tag('thumbnail'))
-        return itemdoc.find(search_path).attrib['url']
-
     def _real_extract(self, url):
         mobj = re.match(self._VALID_URL, url)
         video_id = mobj.group('id')