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· Fix some outdated tests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/nfb.py

@@ -1,9 +1,7 @@
 from __future__ import unicode_literals
 
-import re
-
 from .common import InfoExtractor
-from ..utils import (
+from ..compat import (
     compat_urllib_request,
     compat_urllib_parse,
 )
@@ -12,7 +10,7 @@ from ..utils import (
 class NFBIE(InfoExtractor):
     IE_NAME = 'nfb'
     IE_DESC = 'National Film Board of Canada'
-    _VALID_URL = r'https?://(?:www\.)?(nfb|onf)\.ca/film/(?P<id>[\da-z_-]+)'
+    _VALID_URL = r'https?://(?:www\.)?(?:nfb|onf)\.ca/film/(?P<id>[\da-z_-]+)'
 
     _TEST = {
         'url': 'https://www.nfb.ca/film/qallunaat_why_white_people_are_funny',
@@ -32,10 +30,10 @@ class NFBIE(InfoExtractor):
     }
 
     def _real_extract(self, url):
-        mobj = re.match(self._VALID_URL, url)
-        video_id = mobj.group('id')
-
-        page = self._download_webpage('https://www.nfb.ca/film/%s' % video_id, video_id, 'Downloading film page')
+        video_id = self._match_id(url)
+        page = self._download_webpage(
+            'https://www.nfb.ca/film/%s' % video_id, video_id,
+            'Downloading film page')
 
         uploader_id = self._html_search_regex(r'<a class="director-link" href="/explore-all-directors/([^/]+)/"',
                                               page, 'director id', fatal=False)