CLOUDSTACK-7195: log wide exceptions in security_group.py

Some try/except in security_group.py catch a lot of exceptions. There
was already one fixed in CLOUDSTACK-1052. Here is another one. We use
logging.exception() to log those exceptions.

Signed-off-by: Vincent Bernat <Vincent.Bernat@exoscale.ch>
Signed-off-by: Pierre-Luc Dion <pdion891@apache.org>