Incorrect swagger for discriminator

https://github.com/Azure/azure-rest-api-specs/blob/master/specification/recoveryservicessiterecovery/resource-manager/Microsoft.RecoveryServices/stable/2016-08-10/service.json#L8290

Per swagger 2, the `discriminator` _must_ reference a property defined within the declaring type. In this case, the `discriminator` is `instanceType` which is defined in the child type. This is malformed and must be fixed.

Open specification/recoveryservicessiterecovery/resource-manager/Microsoft.RecoveryServices/stable/2016-08-10/service.json around line 8290 and review the declaring and child types against the Swagger 2 discriminator requirement. Confirm the specification passes the repository’s validation checks and that the discriminator references a property defined by the declaring type.

Written by the indexing model from the issue text.