eliminate retries inside of _ensure_default_security_group
eliminate retries inside of _ensure_default_security_group

Since we have to worry about REPEATABLE READ and have logic to
deal with that by throwing a RetryRequest, let's just simplify
the code and eliminate the other retry mechanism completey.

Related-bug: #1475938
Change-Id: I0aab460f60e690a369f09d59a75bb4ca5a7c33f6

huntxu/neutron,dims/neutron,mahak/neutron,wolverineav/neutron,noironetworks/neutron,huntxu/neutron,sebrandon1/neutron,cloudbase/neutron,cloudbase/neutron,eayunstack/neutron,igor-toga/local-snat,klmitch/neutron,sebrandon1/neutron,igor-toga/local-snat,openstack/neutron,openstack/neutron,wolverineav/neutron,mahak/neutron,dims/neutron,bigswitch/neutron,MaximNevrov/neutron,eayunstack/neutron,klmitch/neutron,MaximNevrov/neutron,bigswitch/neutron,noironetworks/neutron,openstack/neutron,mahak/neutron