Fix imports and general cleanup

· Import from compat what comes from compat. Yes, some names are available in utils too, but that's an implementation detail.
· Use _match_id consistently whenever possible
· Fix some outdated tests
· Use consistent valid URL (always match the whole protocol, no ^ at start required)
· Use modern test definitions

youtube_dl/extractor/vbox7.py

@@ -1,19 +1,18 @@
 # encoding: utf-8
 from __future__ import unicode_literals
 
-import re
-
 from .common import InfoExtractor
-from ..utils import (
+from ..compat import (
     compat_urllib_parse,
     compat_urllib_request,
-
+)
+from ..utils import (
     ExtractorError,
 )
 
 
 class Vbox7IE(InfoExtractor):
-    _VALID_URL = r'http://(www\.)?vbox7\.com/play:(?P<id>[^/]+)'
+    _VALID_URL = r'http://(?:www\.)?vbox7\.com/play:(?P<id>[^/]+)'
     _TEST = {
         'url': 'http://vbox7.com/play:249bb972c2',
         'md5': '99f65c0c9ef9b682b97313e052734c3f',
@@ -25,8 +24,7 @@ class Vbox7IE(InfoExtractor):
     }
 
     def _real_extract(self, url):
-        mobj = re.match(self._VALID_URL, url)
-        video_id = mobj.group('id')
+        video_id = self._match_id(url)
 
         redirect_page, urlh = self._download_webpage_handle(url, video_id)
         new_location = self._search_regex(r'window\.location = \'(.*)\';',