Keystore 2.0: Enforce MAX_BOOT_LEVEL in software

Test: Initialize keystore.boot_level in init.rc; then
      adb setprop keystore.boot_level 40 and check logs
Test: Test program creates key with MAX_BOOT_LEVEL tag; ensure
      it can be used before bumping keystore.boot_level but not after
Bug: 176450483
Change-Id: I94ea178e0fd524bf0a5d65b016559ddd7766205f
9 files changed