RecoverySnapshotStorage: silence log spam from file not found

This condition is expected before an LSKF is set, so downgrade it from
ERROR level with stacktrace to INFO.  Also switch from Log to Slogf, as
this avoids needing to format the string separately.

Flag: EXEMPT bug fix
Bug: 372499066
Test: atest FrameworksServicesTests:com.android.server.locksettings.recoverablekeystore
Change-Id: I8cdadbf95229e5f23163fb9171c068ced842d93e