Fix rule not found error in sec grp default rule API

In V2.1 "os-security-group-default-rules", when default rule is not
found then, DB raise exception - 'SecurityGroupDefaultRuleNotFound'.

Further SecurityGroupAPI->get_all_default_rules() try to catch
'NotFound' exception where it would not be able to catch DB raised
exception because that is derived from 'Invalid' exception.

So during not found situation, SecurityGroupDefaultRulesController
should try to catch 'SecurityGroupDefaultRuleNotFound' instead of
'SecurityGroupNotFound'.

Currently 500 error is thrown in not found case.

This patch also catch those exception in V2 API.

Partially implements blueprint v2-on-v3-api

Change-Id: Ib1c5a02ae19c872afb90e79ad13be8d39394ba97
Merge "Fix rule not found error in sec grp default rule API"