Handle Openstack 404 Errors

Openstack can be configured to return 404 errors for certain API requests.  The
one that has been encountered is when Openstack Neutron is configured with the
NoOpFirewall handler.  In this case, calls to get_security_groups will return a
404 HTTP error.

ManageIQ codebase does not handle non-successful API HTTP return codes.  This is
an attempt to simply ignore (and log) any 404 return codes.

https://bugzilla.redhat.com/show_bug.cgi?id=1140191
honestly, I'm a bit wary of doing the whole dynamic lookup of the service NotFound error type, but I couldn't think of another way to do it.  Also, in irb I tried every openstack service that Fog supports for this lookup of the error class, and didn't hit any errors.