Use EncryptorSource::CreateEncryptor for encryptor creation.
EncryptorSource no longer owns the created encryptor.
Change-Id: I34d1f32262b7692bcb347d3b084fd06cbae7850f
FixedEncryptorSource takes hardcoded key id and content key.
Implemented an AES Encryptor using OpenSSL.
Change-Id: I59ba9a41fc0f40925d697045dd1b147b7351c2f9