Add encryption convenience methods to KeystoreClient.

This Cl adds authenticated encryption and decryption methods which
require minimal inputs. These methods are suitable for encrypting local
state on brillo.

BUG: 23528174
TEST=manual using the keystore_cli_v2 tool

Change-Id: I41abcd77452e86b1eb7373f9db95b645100e2f0f
7 files changed
tree: 2a6e7b1e61c7ebd24dc805697d70b4ed2062908e
  1. keystore/
  2. keystore-engine/
  3. softkeymaster/