remove unrequired sleep. add require statement
at_exit only store buckets if have @buckets_storage and @buckets
disable test for ENV["FLUIDFEATURES_USER_FEATURES_FROM_API"]

Things do not seem to be mocked correctly. This is a non-user
feature only used for testing.
fix "100th user hole in feature selection" bug

fix issue where every 100th user would not be assigned features
on percentage basis
v0.6.1