Add `su_key`, a keystore2_key namespace for `su`.

Add a keystore2_key namespace that can be used by `su` for testing.

Test: keystore2_test
Bug: 158500146
Bug: 160623310
Bug: 159466840
Change-Id: I017a10ad8c7fce28e8bc921b764e65c49bae5107
Merged-In: I017a10ad8c7fce28e8bc921b764e65c49bae5107
3 files changed