Trigger specific SGH functions in NetworkManager

    Instead of calling trigger_security_group_members_refresh,
    have NetworkManager and derived classes call more specific
    methods when an instance is created or destroyed.

    Methods such as the trigger_instance_add_security_group_refresh
    and trigger_instance_remove_security_group_refresh,
    instead of just having trigger_security_group_members_refresh
    get called and forcing implementors to try and figure out if
    it's an add or delete