Make Settings aware of legacy user keys with secret key prefix

Secret keys are not longer identifiable by their alias prefix.
So now we call getKeyCharacteristics and check the algorithm of the
key.

Bug: 63931634
Test: Manually installed a key and checked that it is still dispayed
      correctly.
Change-Id: I55a4e46434618cb52ceb9456f184e004165872fd
2 files changed