Keystore 2.0 SPI: Make LockSettingsService tolerate the Keystore 2.0 SPI

This patch adds support for using the Legacy Keystore provider when the
Keystore 2.0 provider is installed. This is the first step
towards the transition to Keystore 2.0.

Installation of the new provider can be triggered by setting the
platform property ro.android.security.keystore2.enable=true.

Bug: 171305115
Test: The system still boots with and without the new SPI being
      installed. And users can still unlock the phone.
Change-Id: I6e92a08a6b3145891585a134c195c4e29be709b5