Add an isTransient() or something similar to TenantSecurityException

[skeet70]

Adding an isTransient() method to TenantSecurityException would make it a lot more convenient for consumers of the library to know if they should retry an operation or not.

The major unknown would be what to do for things that are on the borderline, like a KMS auth error, which may go away on retry if the tenant happens to change something on the KMS side, but likely won't until a later time.