Strip source dir from file comments

Some programs like sphinx emit absolute paths in error messages. Those
cannot be processed by zuul so filter them if they're part of
zuul.project.

Change-Id: Ie8af91017c26f39c3aa9ca098d4230f0688351ce

roles/tox/library/tox_parse_output.py

@@ -105,6 +105,12 @@ def extract_file_comments(tox_output, tox_envlist):
         # Don't report if the file path isn't valid
         if not os.path.isfile(file_path):
             continue
+
+        # Strip current working dir to make absolute paths relative
+        cwd = os.getcwd() + '/'
+        if file_path.startswith(cwd):
+            file_path = file_path[len(cwd):]
+
         ret.setdefault(file_path, [])
         if tox_envlist:
             message = "{envlist}: {message}".format(