Save mConfirmingCredentials state

Fixes: 162486392
Test: Remove all fingerprints/credentials, tap fingerprint settings,
      rotate device when setting credential. Finish credential
      setup and biometric enrollment. Only prompted to set up credential
      once.
Test: 1) Wipe device
      2) Proceed to set up credential in SUW, but pause on first
         credential screen (choose lock)
      3) adb shell cmd uimode night yes // triggers activity recreate
      4) Proceed with credential/biometric setup
      Notice not re-prompted for credentials
Change-Id: I65fc0265acad98b18b152070b85cc4f71693cc68