undefined method `flavors' for #<Fog::Rackspace::Networking::Mock:0x007f89391d6ba8> (NoMethodError)

The failure happens randomly, but it always happens on some machines
and never on some others. I think that the build system is
non-deterministic and success or failure depends on some unknown
variable like filesystem ordering.

Full log and more details here https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=842607