Use https and http appropriately when connecting to MusicBrainz

Fixed some bugs:
- MusicBrainz submit URL always has https as protocol: hardcoded, even when
inappropriate. It's just a graphical issue.
- Whipper appears to always communicate with MusicBrainz using musicbrainzngs
over http. The musicbrainzngs.set_hostname(server).
- `musicbrainzngs.set_hostname(server)` always defaults to http. Since musicbrainzngs
version 0.7 the method `set_hostname` takes an optional argument named `use_https`
(defaults to False) which whipper never passes.

Changed behaviour of `server` option (`musicbrainz` section of whipper's configuration file).
Now it expects an URL with a valid scheme (scheme must be `http` or `http`, empty scheme isn't allowed anymore).
Only the scheme and netloc parts of the URL are taken into account.

Fixes #437.

Signed-off-by: JoeLametta <JoeLametta@users.noreply.github.com>

whipper/common/config.py

@@ -75,11 +75,12 @@ class Config:
     # musicbrainz section
 
     def get_musicbrainz_server(self):
-        server = self.get('musicbrainz', 'server') or 'musicbrainz.org'
-        server_url = urlparse('//' + server)
-        if server_url.scheme != '' or server_url.path != '':
-            raise KeyError('Invalid MusicBrainz server: %s' % server)
-        return server
+        conf = self.get('musicbrainz', 'server') or 'https://musicbrainz.org'
+        if not conf.startswith(('http://', 'https://')):
+            raise KeyError('Invalid MusicBrainz server: unsupported '
+                           'or missing scheme')
+        scheme, netloc, _, _, _, _ = urlparse(conf)
+        return {'scheme': scheme, 'netloc': netloc}
 
     # drive sections