Model validation will fail for CB cases

[slahabar]

In RLClientLib/vw_model/vw_model.cc the default value for MODEL_VW_INITIAL_COMMAND_LINE is changed to CCB. The default behavior has now changed for cb. The compatibility check for APS model s will always fail.

Change the default command line to cb.

[jackgerrits]

When there is no model for CB, it does not use the safe_vw factory. It instead uses an explicit explore only mode. See here: https://github.com/VowpalWabbit/reinforcement_learning/blob/bf4d7bb54b79703831b46af74edbd7047d4fa5af/rlclientlib/live_model_impl.cc#L64