Restore name of MockCertificateModel

[james-ball-qualcomm]

Was change by @dhower-qc in #271

[james-ball-qualcomm]

I see I had a model key in Certificate Models but it wasn't used anywhere so I removed it. I also updated the schema to remove model and then changed the model name to be any string that can be a hash key (copied from model class schema). The idea is that a certificate class has a particular naming scheme for models in that certificate class so just because MC100 has a naming convention that MC is the class name and 100 is the model number, you can't assume this for all certificate models. In particular, the MockCertificateClass has no naming convention for its certificate models so this provides the necessary coverage.