Fix incorrect parse of url in video_module.py

Sometimes the video url may look like 'http://abc.com/path/video.mp4?xxxx'.
(For example, the Windows Azure's media service will offer such type of url.)
The original code in video_module.py will produce 'mp4?xxxx' instead of 'mp4'
as the extension of a filename for such type of url, and therefore the video
will be non-playable. The fix here uses the built-in urlparse module to retrive
only the path component from a url and therefore the extension 'mp4' will be
correctly fetched.

common/lib/xmodule/xmodule/video_module/video_module.py

@@ -43,6 +43,7 @@ from .video_utils import create_youtube_string
 
 from xmodule.modulestore.inheritance import InheritanceKeyValueStore
 from xblock.runtime import KvsFieldData
+from urlparse import urlparse
 
 log = logging.getLogger(__name__)
 
@@ -253,7 +254,8 @@ class VideoModule(VideoFields, XModule):
         track_url = None
         transcript_download_format = self.transcript_download_format
 
-        get_ext = lambda filename: filename.rpartition('.')[-1]
+        # Prevent incorrectly parsing urls like 'http://abc.com/path/video.mp4?xxxx'.
+        get_ext = lambda filename: urlparse(filename).path.rpartition('.')[-1]
         sources = {get_ext(src): src for src in self.html5_sources}
 
         if self.download_video: