Keystore 2.0: Implement legacy blob support.

This CL implements on-demand migration of legacy key blobs into
the Keystore 2.0.

This CL has joined authorship by
hasinigt@google.com and jdanis@google.com

Test: keystore2_test
      CTS Test.
      And manual test with key upgrade app.
Change-Id: I0a1f266c12f06cc2e196692d759dedf48b4d347a
10 files changed