Merge from widevine of http://go/wvgerrit/14744
The OEMCrypto unit test TestSignatureBoth verifies that a cast
certificate cannot be used to derive session keys. This CL relaxes
the requirement that DeriveKeysFromSessionKey returns a specific error
code instead of just failing.
bug: 21708882
Change-Id: I4163a9616122ad709bab76f488d030239029861c