Merge from widevine repo of http://go/wvgerrit/21521
On devices that use provisioning 3.0, the function
OEMCrypto_GenerateSignature will only be used for a license renewal.
This CL adds a call to OEMCrypto_GenerateSignature to the refresh key
tests. Otherwise, there would be no coverage at all for that
function.
Change-Id: Icbd568eea3f9f256cc9b0b441f7907b316bb5b69