Remove any non alphanum character present in email for username

membership/models.py

@@ -105,6 +105,9 @@ def assign_username(user):
                 logger.debug("Inferred username from name is empty. So, "
                              "inferring from email now.")
                 user.username = user.email[0:user.email.index("@")]
+                user.username = "".join(
+                    [char for char in user.username if char.isalnum()]
+                ).lower()
             except Exception as ex:
                 logger.debug("Exception %s" % str(ex))
                 user.username = get_random_string(