Also include snapshot value in APK cache digest.

We've seen evidence where a runtime restart may have occurred while
a device was still transitioning between isolated storage states; to
ensure that parsed APKs are always invalidated correctly, include
the snapshot state of current boot in the digest.

Bug: 124385369
Test: manual
Change-Id: Ia8d4b5466ae802c31e719c2bc798642c6c73e6c3