Make generateKey() return a status

This change adds some integers to the AIDL interface in order to convey
status back to the caller of generateKey(). This will inform the caller
as to whether or not the errors that may occur during provisioning are
permanent, and if not, what to do with the transient error.

Bug: 227306369
Test: RemoteProvisionerUnitTests
Change-Id: I9202358a102b0fb0a104525632a005acb7355840
4 files changed