Avoid misleading log messages about failed to find key [v2]

If a user's CE storage requires a secret to unlock, then there's no need
to try to unlock it without one.

This avoids logging some misleading error messages on every boot, like:

    E vold    : Failed to read from /data/misc/vold/user_keys/ce/0/current/keymaster_key_blob: No such file or directory
    E vold    : Failed to find working ce key for user 0
    E vold    : Couldn't read key for 0

This is a fixed version of http://ag/13879239, which broke
Resume on Reboot.

Bug: 146206679

Test: Verified that the misleading log message is no longer present when
      booting a device with a PIN.

      Also on Cuttlefish, ran 'atest \
            com.android.server.am.UserControllerTest \
            com.android.cts.devicepolicy.MixedManagedProfileOwnerTest#testResetPasswordWithToken \
            FrameworksServicesTests:RebootEscrowDataTest \
            FrameworksServicesTests:LockSettingsServiceTests \
            FrameworksServicesTests:RecoverySystemServiceTest \
            FrameworksServicesTests:RebootEscrowManagerTests \
            FrameworksServicesTests:RebootEscrowProviderServerBasedImplTests'

      Also on Cuttlefish, verified that Userspace Reboot wasn't broken:
        adb shell locksettings set-pin 1234
        adb reboot
        adb shell dumpsys activity | grep 'User.*state=' # shows RUNNING_LOCKED
        adb shell input text 1234
        adb shell input keyevent 66
        adb shell dumpsys activity | grep 'User.*state=' # shows RUNNING_UNLOCKED
        adb reboot userspace
        adb shell dumpsys activity | grep 'User.*state=' # shows RUNNING_UNLOCKED
        adb logcat -d | grep 'CE storage' # shows "CE storage for users [0] is already unlocked"

      Also on Bramble, verified that Resume on Reboot wasn't broken:
        adb shell locksettings set-pin 1234
        adb reboot
        adb shell dumpsys activity | grep 'User.*state=' # shows RUNNING_LOCKED
        adb shell cmd recovery request-lskf ota
        adb shell input text 1234
        adb shell input keyevent 66
        adb shell dumpsys activity | grep 'User.*state=' # shows RUNNING_UNLOCKED
        adb shell cmd recovery reboot-and-apply ota 1
        adb shell dumpsys activity | grep 'User.*state=' # shows RUNNING_UNLOCKED

Change-Id: I482ed8017f7bbc8f7d4fd5a2c0f58629317ce4ed