always look for the .gitreview file in root of repo

The build may not be happening in the root of the repository, so look
for that directory explicitly before trying to read the .gitreview
file.

Change-Id: I75e952c567d8387d3c620a2b005474ad2441f086
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

openstackdocstheme/ext.py

@@ -124,9 +124,18 @@ def _get_series_name():
     "Return string name of release series, or 'latest'"
     global _series
     if _series is None:
+        try:
+            git_root_dir = subprocess.check_output(
+                ['git', 'rev-parse', '--show-toplevel'],
+            ).decode('utf-8').strip()
+        except Exception:
+            logger.warning('Cannot find git top directory, assuming "."')
+            git_root_dir = '.'
         parser = configparser.ConfigParser()
-        # TODO(stephenfin): Should this be relative to some directory?
-        parser.read('.gitreview')
+        in_file = os.path.join(git_root_dir, '.gitreview')
+        parsed = parser.read(in_file)
+        if not parsed:
+            logger.info('No {} found'.format(in_file))
         try:
             branch = parser.get('gerrit', 'defaultbranch')
         except configparser.Error: