Merge from widevine repo of http://go/wvgerrit/21682
This CL updates oemcrypto/test/oec_device_features.cpp to figure out
the provisioning method and filter out tests that are not relevant to
the device's method.
This CL also introduces unit tests for GetOEMPublicCertificate.
Unit tests for RewrapDeviceRSAKey30 will be in a future CL.
Change-Id: Ib7065ce866d1171ca61b9aa08188fa2ac8d90fc2