[FIX] runbot_cla: fix enforce utf-8 even when runbot locale is different

The CLA md file must be encoded in UTF-8 but before this commit, the
file was opened with the locale of the system running the runbot. That
way, a UnicodeDecodeError was raised when the CLA was UTF-8 and not the
runbot locale was different. Leading to wrong validations.

This commit enforce UTF-8 encoding when opening the CLA's.

runbot_cla/runbot.py

@@ -1,6 +1,7 @@
 # -*- encoding: utf-8 -*-
 
 import glob
+import io
 import logging
 import re
 
@@ -24,7 +25,7 @@ class runbot_build(models.Model):
                     state = "success"
                 else:
                     try:
-                        cla = ''.join(open(f).read() for f in cla_glob)
+                        cla = ''.join(io.open(f,encoding='utf-8').read() for f in cla_glob)
                         if cla.lower().find(email) != -1:
                             state = "success"
                     except UnicodeDecodeError: