* Define exceptions BayModelNotFound and BayModelAlreadyExists. These
two exceptions were used in the code but not defined.
* Remove methods reserve_baymodel and release_baymodel, since it
does not make sense to reserve/release a baymodel.
* Remove exception BayModelAssociated. This exception was used without
being defined and does not make sense for baymodel.
* Remove unrelated code at method create_baymodel.
Change-Id: I6946d771d40c5274f59b94d17542d84685c26e27