Fix flake8 issues related to the use of global

Change-Id: I65ff4d136a5a7ca324d0cda6bba9063dd4d1b99d
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/osm_nbi/nbi.py b/osm_nbi/nbi.py
index 4e7e8ee..17c7c15 100644
--- a/osm_nbi/nbi.py
+++ b/osm_nbi/nbi.py
@@ -2427,7 +2427,6 @@
     Set database, storage, message configuration
     Init database with admin/admin user password
     """
-    global nbi_server
     global subscription_thread
     global cef_logger
     global current_backend