GUI-836: Prevent 404 error when updating a security group that has a deleted security group in one of its rules

Also wrap calls to update_rules and update_tags in standard error handler to display errors from API calls.

Fixes https://eucalyptus.atlassian.net/browse/GUI-836

Note that when a security group that has a rule with a deleted security group is saved, the updated security group will no longer contain the rule with the deleted security group, which is the expected behavior IMHO.